Deprecate Python:acquire_gil and use Python::with_gil.

[ghuls]

Problem Description

Deprecate Python:acquire_gil and use Python::with_gil instead as PyO3 recommends this now:

PyO3/pyo3#2549

[ghuls]

Working on it.

[ritchie46]

Awesome. I recall that we could not make all work without Python::acquire_gil when I tried that earlier. I wonder what the recommended approach for those cases is.

Let's first find out on which snippets that is the case, then we can ask a more useful question.

[ghuls]

The only issue I found is in pub fn get_mmap_bytes_reader<'a>(py_f: &'a PyAny) -> PyResult<Box<dyn MmapBytesReader + 'a>> { as it returns multiple types.