[red-knot] understand equivalence of specialized generic classes

Observed by @cake-monotone in https://github.com/astral-sh/ruff/pull/17174#discussion_r2046229239

```py
from knot_extensions import is_subtype_of, static_assert

class A[T]:
    pass

class B(A[int]):
    pass

static_assert(is_subtype_of(B, A[int]))  # fails, but should pass
```

[Playground](https://types.ruff.rs/e3a48a7c-b17d-4a6d-977b-7fbf0d0ec1f3)