[ty] Narrow bound method overloads by receiver (#24707)
## Summary
Given:
```python
from typing import overload
class Base:
@overload
def convert(self: "Base", x: int) -> int: ...
@overload
def convert(self: "Child", x: str) -> str: ...
def convert(self, x: int | str) -> int | str:
return x
class Child(Base): ...
```
On main, we treat `Base().convert` as if both overloads are still
possible, including the overload that requires `self: "Child"`.
After this PR:
```python
reveal_type(Base().convert)
# bound method Base.convert(x: int) -> int
reveal_type(Child().convert)
# Overload[(x: int) -> int, (x: str) -> str]
```
So `Base().convert("x")` is no longer considered valid via narrowing on
the actual receiver type.
Closes https://github.com/astral-sh/ty/issues/2693.
Closes https://github.com/astral-sh/ty/issues/2612.
Closes https://github.com/astral-sh/ty/issues/3380.
Closes https://github.com/astral-sh/ty/issues/1169.
