Improve tests of `typing.override`

[sobolevn]

Right now we have several things to improve:

1. This branch is not covered by tests:

   cpython/Lib/typing.py

   Line 3490 in 4c87537

   pass

   We don't have a single test that ensures that @override will not fail for some weird cases. Since 99.99% of use-cases will simply be @override def some(...): ..., it is not very important - but still desirable
2. We don't test @classmethods, I guess it is special enough to be included
3. @property is also missing from tests, but is mentioned in PEP: https://peps.python.org/pep-0698/#specification and https://peps.python.org/pep-0698/#limitations-of-setting-override
4. PEP also mentions @functools.lru_cache and similar decorators as an example of how wrappers should be nested. Why don't we test it? Right now there are no tests for nested method decorators (except staticmethod)
5. It might not hurt to test that parent's methods definitions are not mutated (I think this is a part of the contract)

PR is on its way :)

Linked PRs

• gh-102324: Improve tests of typing.override #102325