BUG: Disallow shadowed modulenames

[charris]

Backport of #25181 and #25185.

This is a better version of #25114.
Closes #22819. Closes #25182.
Enforces the following:

• Warns (but doesn't break, for BC) when -m is passed with a .pyf in a -c call, the name is ignored and taken from the .pyf file (the only logical option)
• Each -c run will only produce one python module, so there can only be one .pyf file
• Will not write out ambiguous wrapper files when -m is passed without -c and .pyf files are present (new, BUG: f2py generates incorrect wrapper files when passed -m and a .pyf #25182)

For the last point -m blah is internally replaced with -m modname from the .pyf file, so no additional (incorrect) wrappers are produced.

There already is a note in the documentation, but this is a much better solution (and also paves the way for #25111). The documentation could probably use an update, and since this is technically a user facing change it might need a release note.

[charris]

This seems to have a prerequisite backport. Will wait until more go in and rebase.

[charris]

@HaoZeke Any ideas as to what is needed for this to work? It seems related to using the meson backend, but the meson.build.template file is not part of the compiled numpy. I'm guessing numpy is not compiled with meson in these failing tests.

[HaoZeke]

@HaoZeke Any ideas as to what is needed for this to work? It seems related to using the meson backend, but the meson.build.template file is not part of the compiled numpy. I'm guessing numpy is not compiled with meson in these failing tests.

Yeah the problem is that test doesn't need to have --backend meson I guess. Although on 3.9 it should have been skipped, will update the skipif.

[charris]

I think it might have been in numpy/f2py/setup.py. Lets see if this fixes things:

-        'backends/meson.build.template',
+        '_backends/meson.build.template',

[HaoZeke]

I think it might have been in numpy/f2py/setup.py. Lets see if this fixes things:

-        'backends/meson.build.template',
+        '_backends/meson.build.template',

In general #25210 is better, runs the same test for filename on distutils and meson, so that's an option too. Though the typo definitely should be fixed!