Function pyo3::gil::gil_is_acquired

fn gil_is_acquired() -> bool

Checks whether the GIL is acquired.

Note: This uses pyo3’s internal count rather than PyGILState_Check for two reasons:

1. for performance
2. PyGILState_Check always returns 1 if the sub-interpreter APIs have ever been called, which could lead to incorrect conclusions that the GIL is held.