Generalize `path_t` for C level optimizations

[nineteendo]

Feature or enhancement

Proposal:

Quoting @eryksun:

The implementation of path_t could be generalized to support fields to configure the converter to use wide regardless of platform, to allow null characters, to allow arbitrary length paths (e.g. no 32767 length limit on Windows), and a new field such as bytes_input to determine whether a path result has to be converted back to bytes. The option to always use a wide-character path is a generalization of the current behavior on Windows. Argument Clinic would be extended to support the new options. The implementations of _path_splitroot_ex(), _path_normpath(), and _path_abspath() (if adopted) would benefit, and also the _path_is*() helpers on Windows.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

• gh-102511: Add C implementation of os.path.splitroot() #118089

Linked PRs

• gh-118263: Generalize path_t for C level optimizations #118355
• [3.13] gh-118263: Add additional arguments to path_t (Argument Clinic type) in posixmodule (GH-118355) #119513
• [3.12] gh-118263: Add additional arguments to path_t (Argument Clinic type) in posixmodule (GH-118355) #119608

[nineteendo]

cc @zooba, @serhiy-storchaka Sorry for the ping, I couldn't wait on your response, so I implemented it on my own.