Update default and latest Python versions for 3.14 (#20725)

Summary
--

Closes #19467 and also removes the warning about using Python 3.14
without
preview enabled.

I also bumped `PythonVersion::default` to 3.9 because it reaches EOL
this month,
but we could also defer that for now if we wanted.

The first three commits are related to the `latest` bump to 3.14; the
fourth commit
bumps the default to 3.10.

Note that this PR also bumps the default Python version for ty to 3.10
because
there was a test asserting that it stays in sync with
`ast::PythonVersion`.

Test Plan
--

Existing tests

I spot-checked the ecosystem report, and I believe these are all
expected. Inbits doesn't specify a target Python version, so I guess
we're applying the default. UP007, UP035, and UP045 all use the new
default value to emit new diagnostics.

crates/ty_python_semantic/resources/mdtest/attributes.md

@@ -2109,7 +2109,7 @@ All attribute access on literal `bytes` types is currently delegated to `builtin
 ```py
 # revealed: bound method Literal[b"foo"].join(iterable_of_bytes: Iterable[@Todo(Support for `typing.TypeAlias`)], /) -> bytes
 reveal_type(b"foo".join)
-# revealed: bound method Literal[b"foo"].endswith(suffix: @Todo(Support for `typing.TypeAlias`) | tuple[@Todo(Support for `typing.TypeAlias`), ...], start: SupportsIndex | None = ellipsis, end: SupportsIndex | None = ellipsis, /) -> bool
+# revealed: bound method Literal[b"foo"].endswith(suffix: @Todo(Support for `typing.TypeAlias`) | tuple[@Todo(Support for `typing.TypeAlias`), ...], start: SupportsIndex | None = EllipsisType, end: SupportsIndex | None = EllipsisType, /) -> bool
 reveal_type(b"foo".endswith)
 ```
 

crates/ty_python_semantic/resources/mdtest/binary/classes.md

@@ -18,6 +18,11 @@ reveal_type(A | B)  # revealed: UnionType
 
 ## Union of two classes (prior to 3.10)
 
+```toml
+[environment]
+python-version = "3.9"
+```
+
 ```py
 class A: ...
 class B: ...

crates/ty_python_semantic/resources/mdtest/call/getattr_static.md

@@ -57,7 +57,7 @@ We can access attributes on objects of all kinds:
 import sys
 
 reveal_type(inspect.getattr_static(sys, "dont_write_bytecode"))  # revealed: bool
-# revealed: def getattr_static(obj: object, attr: str, default: Any | None = ellipsis) -> Any
+# revealed: def getattr_static(obj: object, attr: str, default: Any | None = EllipsisType) -> Any
 reveal_type(inspect.getattr_static(inspect, "getattr_static"))
 
 reveal_type(inspect.getattr_static(1, "real"))  # revealed: property

crates/ty_python_semantic/resources/mdtest/call/methods.md

@@ -651,7 +651,7 @@ static_assert(is_assignable_to(TypeOf[property.__set__], Callable))
 reveal_type(MyClass.my_property.__set__)
 static_assert(is_assignable_to(TypeOf[MyClass.my_property.__set__], Callable))
 
-# revealed: def startswith(self, prefix: str | tuple[str, ...], start: SupportsIndex | None = ellipsis, end: SupportsIndex | None = ellipsis, /) -> bool
+# revealed: def startswith(self, prefix: str | tuple[str, ...], start: SupportsIndex | None = EllipsisType, end: SupportsIndex | None = EllipsisType, /) -> bool
 reveal_type(str.startswith)
 static_assert(is_assignable_to(TypeOf[str.startswith], Callable))
 
@@ -707,7 +707,7 @@ def _(
     # revealed: (instance: object, value: object, /) -> Unknown
     reveal_type(j)
 
-    # revealed: (self, prefix: str | tuple[str, ...], start: SupportsIndex | None = ellipsis, end: SupportsIndex | None = ellipsis, /) -> bool
+    # revealed: (self, prefix: str | tuple[str, ...], start: SupportsIndex | None = EllipsisType, end: SupportsIndex | None = EllipsisType, /) -> bool
     reveal_type(k)
 
     # revealed: (prefix: str | tuple[str, ...], start: SupportsIndex | None = None, end: SupportsIndex | None = None, /) -> bool

crates/ty_python_semantic/resources/mdtest/scopes/moduletype_attrs.md

@@ -97,7 +97,7 @@ inside the module:
 import typing
 
 reveal_type(typing.__name__)  # revealed: str
-reveal_type(typing.__init__)  # revealed: bound method ModuleType.__init__(name: str, doc: str | None = ellipsis) -> None
+reveal_type(typing.__init__)  # revealed: bound method ModuleType.__init__(name: str, doc: str | None = EllipsisType) -> None
 
 # For a stub module, we don't know that `__file__` is a string (at runtime it may be entirely
 # unset, but we follow typeshed here):

crates/ty_python_semantic/resources/mdtest/snapshots/return_type.md_-_Function_return_type_-_Invalid_return_type_…_(c3a523878447af6b).snap

@@ -37,7 +37,7 @@ error[invalid-return-type]: Return type does not match returned value
   |            --- Expected `int` because of return type
 2 |     # error: [invalid-return-type]
 3 |     return ...
-  |            ^^^ expected `int`, found `ellipsis`
+  |            ^^^ expected `int`, found `EllipsisType`
 4 |
 5 | # error: [invalid-return-type]
   |

crates/ty_python_semantic/resources/mdtest/stubs/ellipsis.md

@@ -47,7 +47,7 @@ Iterating over an ellipsis literal as part of a `for` loop in a stub is invalid,
 results in a diagnostic:
 
 ```pyi
-# error: [not-iterable] "Object of type `ellipsis` is not iterable"
+# error: [not-iterable] "Object of type `EllipsisType` is not iterable"
 for a, b in ...:
     reveal_type(a)  # revealed: Unknown
     reveal_type(b)  # revealed: Unknown
@@ -59,13 +59,13 @@ In a non-stub file, there's no special treatment of ellipsis literals. An ellips
 be assigned if `EllipsisType` is actually assignable to the annotated type.
 
 ```py
-# error: 7 [invalid-parameter-default] "Default value of type `ellipsis` is not assignable to annotated parameter type `int`"
+# error: 7 [invalid-parameter-default] "Default value of type `EllipsisType` is not assignable to annotated parameter type `int`"
 def f(x: int = ...) -> None: ...
 
-# error: 1 [invalid-assignment] "Object of type `ellipsis` is not assignable to `int`"
+# error: 1 [invalid-assignment] "Object of type `EllipsisType` is not assignable to `int`"
 a: int = ...
 b = ...
-reveal_type(b)  # revealed: ellipsis
+reveal_type(b)  # revealed: EllipsisType
 ```
 
 ## Use of `Ellipsis` symbol
@@ -73,6 +73,6 @@ reveal_type(b)  # revealed: ellipsis
 There is no special treatment of the builtin name `Ellipsis` in stubs, only of `...` literals.
 
 ```pyi
-# error: 7 [invalid-parameter-default] "Default value of type `ellipsis` is not assignable to annotated parameter type `int`"
+# error: 7 [invalid-parameter-default] "Default value of type `EllipsisType` is not assignable to annotated parameter type `int`"
 def f(x: int = Ellipsis) -> None: ...
 ```