Updates window box default parameters and regenerates clinic headers for py312.

[gotyaoi]

Fixes #50.

[stephanosio]

@gotyaoi #54 fixed the Python 3.10-3.12 CI issues. Could you rebase?

[stephanosio]

It looks like we will need to update the README to say:

1. Avoid manually modifying clinic header files.
2. Run clinic.py on _cursesmodule.c and _curses_panel.c after applying patches.

I will post a follow-up PR doing that.

By the way, I have noticed that the files under the py312 directory were simply copied over from py311 without following the process described in the README, which explains why there are so many header file changes in this PR.

A more complete fix should involve copying _cursesmodule.c and _curses_panel.c from the Python 3.12 tree, applying the windows-curses-specific patches and running clinic.py on them to generate headers.

For now, I will merge this PR as-is and make a new release. If there are still more problems, I will look into implementing the more-complete fix described above.