Type declarations to allow integration with type checking and linting tools about gmpy HOT 2 OPEN

I was planing to add support for return annotations in the __text_signature__. That will allow to describe typing information via docstring. Now this works with the sphinx (see e.g. this), but that information isn't available for introspection with inspect module, for type checkers, etc.

Here is the d.p.o thread: https://discuss.python.org/t/type-signatures-for-extension-modules-pep-draft/43914

One suggestion was: support *.pyi files as a source for the inspect module. Maybe someday I'll find a time to create a feature request.

So, I think *.pyi stub files - a good thing to have.

from gmpy.

See python/cpython#121945, however.

from gmpy.