[BUG] Calling a method on a TypeVar fails

[hmansell]

In this example, mypy succeeds, but pyrefly fails.

https://mypy-play.net/?mypy=latest&python=3.12&gist=5f8fe155f983bdb6950f422aee9cd612 has two examples of calling a method a TypeVar that returns Self.

1. In the case of a TypeVar that lists a union of types, pyrefly doesn't like us calling f() on the variable of type T
2. In the case of a bounded TypeVar, it seems pyrefly says "Returned type B is not assignable to declared return type TypeVar[TBounded]". It seems to be incorrectly inferring that the Self that f() returns is of type B rather than of the type TBounded.

Pyrefly URL:
https://pyrefly.org/sandbox/?code=GYJw9gtgBALgngBwJYDsDmUkQWEMoBUAUEQMYA2AhgM7VQBCAFAJQBcRUnUAJgKbBRgjar3LBmUALQA+KAGVRwdlxVQQvGAFcQKKCLEdVnMlVpQAwo3ptDnBDWomHUACJWbK+7RJEAKlABeKF9EXgA1ShBGWygAIl9YgBoY82SVF2TmEj4BNGiVACNWYMypWV9lLnUtHSgCgDohLL96ME0UPm5A4NCIqJj41vbOpJiCto6A+iJmnKg8seLfIY7eblKZYJXOys5q7V0GpqIgA

[grievejia]

Thanks for the bug report!

Issue 1 requires proper support for constrained typevars.

Issue 2 has an easier repro. Track that separately with #152.