[pyupgrade] Expand UP040 to handle generic functions and classes (UP040, UP046)

[ntBre]

Summary

This PR extends our PEP 695 handling from the type aliases handled by UP040 to generic function and class parameters, as suggested in the latter two examples from #4617:

# Input
T = TypeVar("T", bound=float)
class A(Generic[T]):
    ...

def f(t: T):
    ...

# Output
class A[T: float]:
    ...

def f[T: float](t: T):
    ...

I first implemented this as part of UP040, but based on a brief discussion during a very helpful pairing session with @AlexWaygood, I opted to split them into separate rules in the last 5 commits. From a quick look, and based on this issue, I'm pretty sure neither of these rules is currently in pyupgrade, so I just took the next available code, UP046.

The last main TODO, noted in the rule file and in the fixture, is to handle generic method parameters not included in the class itself, S in this case:

T = TypeVar("T")
S = TypeVar("S")

class Foo(Generic[T]):
    def bar(self, x: T, y: S) -> S: ...

but Alex mentioned that that might be okay to leave for a follow-up PR.

I also left a TODO about handling multiple subclasses instead of bailing out when more than one is present. I'm not sure how common that would be, but I can still handle it here, or follow up on that too.

I think this is unrelated to the PR, but when I ran cargo dev generate-all, it removed the rule code PLW0101 from ruff.schema.json. It seemed unrelated, so I left that out, but I wanted to mention it just in case.

Test Plan

New test fixture, cargo nextest run

[github-actions]

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