[ty] Include synthesized arguments in displayed counts for too-many-positional-arguments (#18098)

## Summary

Resolves [#290](https://github.com/astral-sh/ty/issues/290).

All arguments, synthesized or not, are now accounted for in
`too-many-positional-arguments`'s error message.

For example, consider this example:

```python
class C:
	def foo(self): ...

C().foo(1)  # !!!
```

Previously, ty would say:

> Too many positional arguments to bound method foo: expected 0, got 1

After this change, it will say:

> Too many positional arguments to bound method foo: expected 1, got 2

This is what Python itself does too:

```text
Traceback (most recent call last):
  File "<python-input-0>", line 3, in <module>
    C().foo()
    ~~~~~~~^^
TypeError: C.foo() takes 0 positional arguments but 1 was given
```

## Test Plan

Markdown tests.

crates/ty_python_semantic/src/types/call/bind.rs

@@ -1285,14 +1285,8 @@ impl<'db> Binding<'db> {
                     first_excess_argument_index,
                     num_synthetic_args,
                 ),
-                expected_positional_count: parameters
-                    .positional()
-                    .count()
-                    // using saturating_sub to avoid negative values due to invalid syntax in source code
-                    .saturating_sub(num_synthetic_args),
-                provided_positional_count: next_positional
-                    // using saturating_sub to avoid negative values due to invalid syntax in source code
-                    .saturating_sub(num_synthetic_args),
+                expected_positional_count: parameters.positional().count(),
+                provided_positional_count: next_positional,
             });
         }
         let mut missing = vec![];