Reparametrize implicit generic QuerySet subclasses

[federicobond]

When a custom QuerySet subclass is defined without explicit type parameters (e.g. class MyQS(QuerySet): ...), make it implicitly generic by copying the parent QuerySet's type variables, analogous to the existing reparametrize_any_manager_hook for Manager subclasses.

This enables the annotate plugin hook to propagate annotation type information through custom querysets via copy_modified(args=...), which requires the queryset class to have type variables.

Disclosure: I've used Claude Opus 4.6 to assist in writing this changeset, but I have carefully iterated and manually reviewed the results.

[sobolevn]

Please, test this with explicit disallow_any_generics = True, since your docstring mentions this.

[sobolevn]

Thanks a lot!

[federicobond]

Thank you. Was just about to comment on the new test, got sidetracked.

[UnknownPlatypus]

You are too fast ahah, I also did that in #2776 + a small refactor, I'll extract the refactor, it was rather nice.
Currently both functions are exact duplicates of 35+ lines with only variable names changing

This is what I ended up with:

def reparametrize_any_manager_hook(ctx: ClassDefContext) -> None:
    """
    Add implicit generics to manager classes that are defined without generic.

    Eg.

        class MyManager(models.Manager): ...

    is interpreted as:

        _T = TypeVar("_T", bound=Model, covariant=True)
        _QS = TypeVar("_QS", bound=QuerySet[Any], covariant=True, default=QuerySet[_T])
        class MyManager(models.Manager[_T, _QS]): ...
    """
    reparametrize_generic_class(ctx, fullnames.BASE_MANAGER_CLASS_FULLNAME)


def reparametrize_any_queryset_hook(ctx: ClassDefContext) -> None:
    """
    Add implicit generics to queryset classes that are defined without generic.

    Eg.

        class MyQuerySet(models.QuerySet): ...

    is interpreted as:

        _T = TypeVar("_T", bound=Model, covariant=True)
        class MyQuerySet(models.QuerySet[_T]): ...
    """
    reparametrize_generic_class(ctx, fullnames.QUERYSET_CLASS_FULLNAME)

[federicobond]

Makes sense, I decided not to prematurely abstract without a better understanding of the project, but you have more context than I do.

[UnknownPlatypus]

No worries, thanks for the contribution, this is very useful !