Extend PEP 695 generic class and function rules

[ntBre]

Follow up tasks from #15565

• Rename private type variables in generics (don't make inline generics like [_T])
• Allow multiple base classes for generic classes
• Handle generic methods
• Handle default kwargs for Python >= 3.13
• Unquote type variable forward reference annotations (see below)
• Use string replacements for UP040's autofix too, instead of using the ExprGenerator
• Handle TypeVarTuple generics with Unpack instead of *: class MultipleGenerics(Generic[S, T, Unpack[Ts], P]): ... ¹

Related: #4617, #12542

Footnotes

1. https://github.com/astral-sh/ruff/pull/15565#discussion_r1925489033 ↩

[AlexWaygood]

One other thing that might be nice would be to unquote annotations. E.g. old-style type variables often need to quote their bounds if the bound needs to use a forward reference to a name not yet defined

from typing import Generic, TypeVar

T = TypeVar("T", bound="list[T | None]")

class Foo(Generic[T]):
    var: T

But the bounds for PEP-695 type parameters are lazily evaluated, so there's no need to quote forward references:

>>> class Foo[T: list[T | None]]:
...     var: T
...     
>>> Foo.__type_params__[0].__bound__
list[typing.Optional[T]]