BufferedReader and BufferedWriter cannot be used to determine local
files. For example, users can implement CustomFile to operate on OSS
files, and then use BufferedReader(CustomFile) to achieve the buffered
effect. But fileno method can do it.

Note that unfortunately, compat does expose _inspect as well,
so the import remains (just the definition place moves).

The submoudle numpy.compat._pep440 is removed from the default import of
numpy to reduce the import time. See #22061

LooseVersion is provided by Python distutils, which is going away in
3.12. This PR vendors _pep440 from scipy and uses it as a replacement.
Numpy distutils is not touched, replacing LooseVersion in that package
was considered too risky, and numpy distutils will need to go away when
Python distutils does.

`load_module` is deprecated since python 3.4 and will be removed in python 3.12.
Use `exec_module` instead. Provide a convenience function in `distutils.misc_utils`
instead of `npy_load_module` from `compat.py3k`.

* Remove unnecessary imports and minor fixes

`Path` can now never be none, and `PurePath` is not used and not in `__all__`.

Since we no longer support Python 3.5 and below, this code is unreachable.

As with the rest of `py3k.py`, we leave behind the aliases to prevent breaking downstream code.