Re-add py.typed
A similar issue was fixed for the `transformers` package, too: https://github.com/huggingface/transformers/pull/37022
### Feature request

The motivation for removing py.typed no longer seems to apply.  Would a solution like [this one](https://github.com/huggingface/huggingface_hub/pull/2752) work here?

### Motivation

MyPy support is broken.  As more type checkers come out, such as RedKnot, these may also be broken.  It would be good to be PEP 561 compliant as long as it's not too onerous.

### Your contribution

I can re-add py.typed, but I don't know how to make sur all of the `__all__` files are provided (although you may not need to with modern PyRight).