[ty] Improve diagnostics for invalid exceptions (#21475)

## Summary

Not a high-priority task... but it _is_ a weekend :P

This PR improves our diagnostics for invalid exceptions. Specifically:
- We now give a special-cased ``help: Did you mean
`NotImplementedError`` subdiagnostic for `except NotImplemented`, `raise
NotImplemented` and `raise <EXCEPTION> from NotImplemented`
- If the user catches a tuple of exceptions (`except (foo, bar, baz):`)
and multiple elements in the tuple are invalid, we now collect these
into a single diagnostic rather than emitting a separate diagnostic for
each tuple element
- The explanation of why the `except`/`raise` was invalid ("must be a
`BaseException` instance or `BaseException` subclass", etc.) is
relegated to a subdiagnostic. This makes the top-level diagnostic
summary much more concise.

## Test Plan

Lots of snapshots. And here's some screenshots:

<details>
<summary>Screenshots</summary>

<img width="1770" height="1520" alt="image"
src="https://github.com/user-attachments/assets/7f27fd61-c74d-4ddf-ad97-ea4fd24d06fd"
/>

<img width="1916" height="1392" alt="image"
src="https://github.com/user-attachments/assets/83e5027c-8798-48a6-a0ec-1babfc134000"
/>

<img width="1696" height="588" alt="image"
src="https://github.com/user-attachments/assets/1bc16048-6eb4-4dfa-9ace-dd271074530f"
/>

</details>

crates/ty_python_semantic/resources/mdtest/exception/basic.md

@@ -116,17 +116,18 @@ def silence2[T: (
 
 ## Invalid exception handlers
 
+<!-- snapshot-diagnostics -->
+
 ```py
 try:
     pass
-# error: [invalid-exception-caught] "Cannot catch object of type `Literal[3]` in an exception handler (must be a `BaseException` subclass or a tuple of `BaseException` subclasses)"
+# error: [invalid-exception-caught]
 except 3 as e:
     reveal_type(e)  # revealed: Unknown
 
 try:
     pass
-# error: [invalid-exception-caught] "Cannot catch object of type `Literal["foo"]` in an exception handler (must be a `BaseException` subclass or a tuple of `BaseException` subclasses)"
-# error: [invalid-exception-caught] "Cannot catch object of type `Literal[b"bar"]` in an exception handler (must be a `BaseException` subclass or a tuple of `BaseException` subclasses)"
+# error: [invalid-exception-caught]
 except (ValueError, OSError, "foo", b"bar") as e:
     reveal_type(e)  # revealed: ValueError | OSError | Unknown
 
@@ -278,3 +279,20 @@ def f(x: type[Exception]):
     # error: [possibly-unresolved-reference]
     reveal_type(e)  # revealed: None
 ```
+
+## Special-cased diagnostics for `NotImplemented`
+
+<!-- snapshot-diagnostics -->
+
+```py
+try:
+    # error: [invalid-raise]
+    # error: [invalid-raise]
+    raise NotImplemented from NotImplemented
+# error: [invalid-exception-caught]
+except NotImplemented:
+    pass
+# error: [invalid-exception-caught]
+except (TypeError, NotImplemented):
+    pass
+```

crates/ty_python_semantic/resources/mdtest/snapshots/basic.md_-_Exception_Handling_-_Invalid_exception_ha…_(d394c561bdd35078).snap

@@ -0,0 +1,146 @@
+---
+source: crates/ty_test/src/lib.rs
+expression: snapshot
+---
+---
+mdtest name: basic.md - Exception Handling - Invalid exception handlers
+mdtest path: crates/ty_python_semantic/resources/mdtest/exception/basic.md
+---
+
+# Python source files
+
+## mdtest_snippet.py
+
+```
+ 1 | try:
+ 2 |     pass
+ 3 | # error: [invalid-exception-caught]
+ 4 | except 3 as e:
+ 5 |     reveal_type(e)  # revealed: Unknown
+ 6 | 
+ 7 | try:
+ 8 |     pass
+ 9 | # error: [invalid-exception-caught]
+10 | except (ValueError, OSError, "foo", b"bar") as e:
+11 |     reveal_type(e)  # revealed: ValueError | OSError | Unknown
+12 | 
+13 | def foo(
+14 |     x: type[str],
+15 |     y: tuple[type[OSError], type[RuntimeError], int],
+16 |     z: tuple[type[str], ...],
+17 | ):
+18 |     try:
+19 |         help()
+20 |     # error: [invalid-exception-caught]
+21 |     except x as e:
+22 |         reveal_type(e)  # revealed: Unknown
+23 |     # error: [invalid-exception-caught]
+24 |     except y as f:
+25 |         reveal_type(f)  # revealed: OSError | RuntimeError | Unknown
+26 |     # error: [invalid-exception-caught]
+27 |     except z as g:
+28 |         reveal_type(g)  # revealed: Unknown
+29 | 
+30 | try:
+31 |     {}.get("foo")
+32 | # error: [invalid-exception-caught]
+33 | except int:
+34 |     pass
+```
+
+# Diagnostics
+
+```
+error[invalid-exception-caught]: Invalid object caught in an exception handler
+ --> src/mdtest_snippet.py:4:8
+  |
+2 |     pass
+3 | # error: [invalid-exception-caught]
+4 | except 3 as e:
+  |        ^ Object has type `Literal[3]`
+5 |     reveal_type(e)  # revealed: Unknown
+  |
+info: Can only catch a subclass of `BaseException` or tuple of `BaseException` subclasses
+info: rule `invalid-exception-caught` is enabled by default
+
+```
+
+```
+error[invalid-exception-caught]: Invalid tuple caught in an exception handler
+  --> src/mdtest_snippet.py:10:8
+   |
+ 8 |     pass
+ 9 | # error: [invalid-exception-caught]
+10 | except (ValueError, OSError, "foo", b"bar") as e:
+   |        ^^^^^^^^^^^^^^^^^^^^^^-----^^------^
+   |                              |      |
+   |                              |      Invalid element of type `Literal[b"bar"]`
+   |                              Invalid element of type `Literal["foo"]`
+11 |     reveal_type(e)  # revealed: ValueError | OSError | Unknown
+   |
+info: Can only catch a subclass of `BaseException` or tuple of `BaseException` subclasses
+info: rule `invalid-exception-caught` is enabled by default
+
+```
+
+```
+error[invalid-exception-caught]: Invalid object caught in an exception handler
+  --> src/mdtest_snippet.py:21:12
+   |
+19 |         help()
+20 |     # error: [invalid-exception-caught]
+21 |     except x as e:
+   |            ^ Object has type `type[str]`
+22 |         reveal_type(e)  # revealed: Unknown
+23 |     # error: [invalid-exception-caught]
+   |
+info: Can only catch a subclass of `BaseException` or tuple of `BaseException` subclasses
+info: rule `invalid-exception-caught` is enabled by default
+
+```
+
+```
+error[invalid-exception-caught]: Invalid tuple caught in an exception handler
+  --> src/mdtest_snippet.py:24:12
+   |
+22 |         reveal_type(e)  # revealed: Unknown
+23 |     # error: [invalid-exception-caught]
+24 |     except y as f:
+   |            ^ Object has type `tuple[type[OSError], type[RuntimeError], int]`
+25 |         reveal_type(f)  # revealed: OSError | RuntimeError | Unknown
+26 |     # error: [invalid-exception-caught]
+   |
+info: Can only catch a subclass of `BaseException` or tuple of `BaseException` subclasses
+info: rule `invalid-exception-caught` is enabled by default
+
+```
+
+```
+error[invalid-exception-caught]: Invalid tuple caught in an exception handler
+  --> src/mdtest_snippet.py:27:12
+   |
+25 |         reveal_type(f)  # revealed: OSError | RuntimeError | Unknown
+26 |     # error: [invalid-exception-caught]
+27 |     except z as g:
+   |            ^ Object has type `tuple[type[str], ...]`
+28 |         reveal_type(g)  # revealed: Unknown
+   |
+info: Can only catch a subclass of `BaseException` or tuple of `BaseException` subclasses
+info: rule `invalid-exception-caught` is enabled by default
+
+```
+
+```
+error[invalid-exception-caught]: Invalid object caught in an exception handler
+  --> src/mdtest_snippet.py:33:8
+   |
+31 |     {}.get("foo")
+32 | # error: [invalid-exception-caught]
+33 | except int:
+   |        ^^^ Object has type `<class 'int'>`
+34 |     pass
+   |
+info: Can only catch a subclass of `BaseException` or tuple of `BaseException` subclasses
+info: rule `invalid-exception-caught` is enabled by default
+
+```

crates/ty_python_semantic/resources/mdtest/snapshots/basic.md_-_Exception_Handling_-_Special-cased_diagno…_(a97274530a7f61c1).snap

@@ -0,0 +1,93 @@
+---
+source: crates/ty_test/src/lib.rs
+expression: snapshot
+---
+---
+mdtest name: basic.md - Exception Handling - Special-cased diagnostics for `NotImplemented`
+mdtest path: crates/ty_python_semantic/resources/mdtest/exception/basic.md
+---
+
+# Python source files
+
+## mdtest_snippet.py
+
+```
+ 1 | try:
+ 2 |     # error: [invalid-raise]
+ 3 |     # error: [invalid-raise]
+ 4 |     raise NotImplemented from NotImplemented
+ 5 | # error: [invalid-exception-caught]
+ 6 | except NotImplemented:
+ 7 |     pass
+ 8 | # error: [invalid-exception-caught]
+ 9 | except (TypeError, NotImplemented):
+10 |     pass
+```
+
+# Diagnostics
+
+```
+error[invalid-raise]: Cannot raise `NotImplemented`
+ --> src/mdtest_snippet.py:4:11
+  |
+2 |     # error: [invalid-raise]
+3 |     # error: [invalid-raise]
+4 |     raise NotImplemented from NotImplemented
+  |           ^^^^^^^^^^^^^^ Did you mean `NotImplementedError`?
+5 | # error: [invalid-exception-caught]
+6 | except NotImplemented:
+  |
+info: Can only raise an instance or subclass of `BaseException`
+info: rule `invalid-raise` is enabled by default
+
+```
+
+```
+error[invalid-raise]: Cannot use `NotImplemented` as an exception cause
+ --> src/mdtest_snippet.py:4:31
+  |
+2 |     # error: [invalid-raise]
+3 |     # error: [invalid-raise]
+4 |     raise NotImplemented from NotImplemented
+  |                               ^^^^^^^^^^^^^^ Did you mean `NotImplementedError`?
+5 | # error: [invalid-exception-caught]
+6 | except NotImplemented:
+  |
+info: An exception cause must be an instance of `BaseException`, subclass of `BaseException`, or `None`
+info: rule `invalid-raise` is enabled by default
+
+```
+
+```
+error[invalid-exception-caught]: Cannot catch `NotImplemented` in an exception handler
+ --> src/mdtest_snippet.py:6:8
+  |
+4 |     raise NotImplemented from NotImplemented
+5 | # error: [invalid-exception-caught]
+6 | except NotImplemented:
+  |        ^^^^^^^^^^^^^^ Did you mean `NotImplementedError`?
+7 |     pass
+8 | # error: [invalid-exception-caught]
+  |
+info: Can only catch a subclass of `BaseException` or tuple of `BaseException` subclasses
+info: rule `invalid-exception-caught` is enabled by default
+
+```
+
+```
+error[invalid-exception-caught]: Invalid tuple caught in an exception handler
+  --> src/mdtest_snippet.py:9:8
+   |
+ 7 |     pass
+ 8 | # error: [invalid-exception-caught]
+ 9 | except (TypeError, NotImplemented):
+   |        ^^^^^^^^^^^^--------------^
+   |                    |
+   |                    Invalid element of type `NotImplementedType`
+   |                    Did you mean `NotImplementedError`?
+10 |     pass
+   |
+info: Can only catch a subclass of `BaseException` or tuple of `BaseException` subclasses
+info: rule `invalid-exception-caught` is enabled by default
+
+```