gh-157384: Accept non-ASCII names in PyImport_CreateModuleFromInitfunc()

[itamaro]

The builtin loader info encoded the module name as ASCII, so a non-ASCII spec name failed with UnicodeEncodeError even for multi-phase init modules, which support such names when loaded dynamically. Fall back to UTF-8 and mark the name as non-ASCII, so that multi-phase init works and single-phase init is rejected with the same error as for dynamically loaded extensions.

AI assisted with Claude Fable 5.1

• Issue: PyImport_CreateModuleFromInitfunc(): wrong __name__ for submodules, non-ASCII names rejected, inittab name clashes #157384

[encukou]

Out of curiosity (and to inform future prioritization), did this actually come up in practice?

PyInit is soft-deprecated so I'm not too happy adding features, but yeah, this is a valid bugfix.

As a nitpick, mödul isn't a good test name -- it's always encoded in the source, so the fact that it's a mangled word doesn't help readers; also the following d needs the workaround in the C literals.
Consider "mod\N{MICRO SIGN}_sp", or even "mod\N{SNAKE}_sp"?

[itamaro]

Out of curiosity (and to inform future prioritization), did this actually come up in practice?

no, this didn't come up in the real world, it was something claude flagged while looking into the single-phase init issue.

I don't feel strongly about this fix, if you think it's not worth it, we can drop it.