use ParamSpec for pytest.skip instead of __call__ Protocol attribute

[karlicoss]

This is a more canonical way of typing generic callbacks/decorators
(see https://mypy.readthedocs.io/en/stable/protocols.html#callback-protocols)

This helps with potential issues/ambiguity with __call__ semanics in type checkers -- according to python spec, __call__ needs to be present on the class, rather than as an instance attribute to be considered callable.

This worked in mypy because it didn't handle the spec 100% correctly (in this case this has no negative consequences)

However, ty type checker is stricter/more correct about it and every pytest.skip usage results in:

error[call-non-callable]: Object of type _WithException[Unknown, <class 'Skipped'>] is not callable

For more context, see:

• [ty] Understand classes that inherit from subscripted Protocol[] as generic astral-sh/ruff#17832 (comment)
• https://discuss.python.org/t/when-should-we-assume-callable-types-are-method-descriptors/92938

Testing:

Tested with running mypy against the following snippet:

import pytest
reveal_type(pytest.skip)
reveal_type(pytest.skip.Exception)
reveal_type(pytest.skip(reason="whatever"))

Before the change:

test_pytest_skip.py:2: note: Revealed type is "_pytest.outcomes._WithException[def (reason: builtins.str =, *, allow_module_level: builtins.bool =) -> Never, def (msg: Union[builtins.str, None] =, pytrace: builtins.bool =, allow_module_level: builtins.bool =, *, _use_item_location: builtins.bool =) -> _pytest.outcomes.Skipped]"
test_pytest_skip.py:3: note: Revealed type is "def (msg: Union[builtins.str, None] =, pytrace: builtins.bool =, allow_module_level: builtins.bool =, *, _use_item_location: builtins.bool =) -> _pytest.outcomes.Skipped"
test_pytest_skip.py:4: note: Revealed type is "Never"

After the change:

test_pytest_skip.py:2: note: Revealed type is "_pytest.outcomes._WithException[[reason: builtins.str =, *, allow_module_level: builtins.bool =], Never, def (msg: Union[builtins.str, None] =, pytrace: builtins.bool =, allow_module_level: builtins.bool =, *, _use_item_location: builtins.bool =) -> _pytest.outcomes.Skipped]"
test_pytest_skip.py:3: note: Revealed type is "def (msg: Union[builtins.str, None] =, pytrace: builtins.bool =, allow_module_level: builtins.bool =, *, _use_item_location: builtins.bool =) -> _pytest.outcomes.Skipped"
test_pytest_skip.py:4: note: Revealed type is "Never"

All types are matching and propagated correctly.

[bluetech]

Thanks! This looks good to me. But looking at this again, I wonder if it wouldn't be simpler (in terms of complexity, not in terms of lines of code) to turn these functions into callable classes? Then the Exception is a regular (class) attribute and there should be no typing shenanigans necessary, unless I'm missing something. WDYT?

[bluetech]

Forgot to mention, the CI failures are unrelated and fixed in main -- rebase should take care of it.