[FEA]: Add .pyi files so IDEs can provide autocompletion

[mdboom]

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Area

General cuda-python

Is your feature request related to a problem? Please describe.

Python language servers and type checkers (e.g. pylance, ruff-lsp, pyre, mypy) generally don't import code, so extension modules, such as those from Cython, are opaque to them.

Describe the solution you'd like

If we provided .pyi files alongside our extension modules, these tools would do a better job at type-checking and providing autocompletions etc.

While I have no direct experience with it, cythonbuilder claims to automatically generate them. Other options may include mypy's stubgen or pyright's --create-stub feature.

If that doesn't work, we may be able to generate .pyi alongside most of the generated code by modifying our generator.

~We will also need some way (through CI or the pre-commit hook, if possible) to ensure that the .pyi files are staying in-sync with the .pyx files.~

We probably don't need to check in the .pyi files into the repo if we can generate them at build time (alongside the .cpp files).

Describe alternatives you've considered

No response

Additional context

No response