This is a followup to astral-sh/ruff#22753. Ty should emit abstract-method-in-final-class on G here, but currently does not:

from typing import Protocol, final

class F(Protocol):
    def f(self) -> int: ...

@final
class G(F): ...

The reason why is that all methods on Protocol classes with an explicit non-None return type and a trivial body should be understood as "implicitly abstract". Ty exempts such methods from the rule that would cause us to complain about this method saying it returns int when it actually returns None; that exemption is only sound if we therefore understand the method as being implicitly abstract. We should extract the is_stub_suite function here into a location where it can be reused, and then reuse it in our determination of which methods are abstract on a class if that class is a Protocol class: https://github.com/astral-sh/ruff/blob/22f240dadf58837f9ac55e5f06d591449f620847/crates/ty_python_semantic/src/types/infer/builder.rs#L2404-L2445.

Cc. @charliermarsh