[Feature request] Typing stubs (`.pyi` files)

Thank you for the awesome library!

When wanting to use it in a typed project, I found the package lacking type annotations.
So I created the stubs manually by looking at the `.pyx` and `.pxd` files, because I did not find a tool to generate them automatically 😅.

I'm happy to submit a PR with stubs if you like 😄

