TYP,ENH: Improve typing with the help of ParamSpec

[BvB93]

This PR improves the annotations of a few functions via use of the PEP 612 ParamSpec type, the latter allowing functions to exclusivelly accept *args and **kwargs that are accepted by a wrapped callback.

Mypy's support for PEP 612 is incomplete at this point though, and changes to np.piecewise and np.apply_along_axis are deferred until support for Concatenate is fully implemented (xref python/mypy#8645).

Examples

from typing import TYPE_CHECKING, Callable
from typing_extensions import ParamSpec

P = ParamSpec("P")

def test_func(func: Callable[P, object], *args: P.args, **kwargs: P.kwargs) -> None:
    func(*args, **kwargs)

if TYPE_CHECKING:
    reveal_type(test_func(len, [1]))  # Revealed type is "None"
    reveal_type(test_func(len, [1], "test123"))  # Too many arguments for "test_func"
    reveal_type(test_func(len, [1], test="test123"))  # Unexpected keyword argument "test" for "test_func"

[charris]

Thanks Bas.