Rename Python::with_gil -> with_python ?

[davidhewitt]

An idea with the upcoming free threaded Python around the corner.

Maybe instead of Python::with_gil, a future PyO3 API can just be pyo3::with_python. No functional difference except dropping the GIL name as that won't always be relevant.

e.g.

Python::with_gil(|py| /* do stuff */)

becomes just

with_python(|py| /* do stuff */)

Maybe we include with_python in the prelude, maybe we invite users to import it.

[Icxolu]

Just throwing some alternatives in the room: Python::in_scope or Python::with_token could also be something if we want to keep it as an (associated) method, but without references to the gil.