gh-143883: Add missing named parameters in public PyModExport C bindings

[ngoldbaum]

See the linked issue for details.

• Issue: PyModule_FromSlotsAndSpec and PyModule_GetToken exposed without named parameters #143883

[ngoldbaum]

ping @encukou since you wrote this code originally

[ngoldbaum]

Looks like unrelated CI issues are causing the failures

[encukou]

Thanks for the catch!
While you're here, could you rename the others to module (rather than mod), and add a missing name to docs?
Or let me know if I should take over.

(Failures are indeed unrelated: Ubuntu was down)

[ngoldbaum]

I did some minor wording tweaks in the docs to adapt to the name changes, let me know if you have suggestions there.