gh-123961: Improve curses C API cleanup

[picnixz]

This PR moves some functions closer to where they are needed and adds the traversal and clear functions in prepartion to make the window type a heap type.

Note

I always hated dealing with void pointers so I'm grateful if you carefully check that I didn't introduce some decaying calls or weird stuff. In addition, please check that the names were carefully refactored (the functions look all the same and it's very simple to make typos!).

• Issue: Refactorization of _cursesmodule.c to fix reference leaks #123961

[vstinner]

I don't think that traverse() and clear() methods make sense before window_type becomes a heap type.

[picnixz]

I don't think that traverse() and clear() methods make sense before window_type becomes a heap type.

No you're right but I think it would reduce the diff later. At runtime, they will be unused since the type is not a heap type (so they won't even be called). Whenever a new capsule is created, we just have the check that would be effective at runtime.

if (_PyType_HasFeature(_PyType_CAST(window_type), Py_TPFLAGS_HEAPTYPE)){

But if you prefer to have it in the PR which moves it to a heap type, I can do it.

[picnixz]

Since I don't know when I'll move it to heap types, I'll delay their addition until then.

[vstinner]

LGTM

[vstinner]

Merged, thanks.