In the course of using msgpack in a project I've written some basic type stubs for the parts of the API I'm using.
I don't think it would be too hard to fill out the type stubs for the rest of the API.

Would you accept a PR adding stub files to the package?
Not sure if you have a preference on adding the types to the code itself or keeping them as separate stub files.

related: https://www.python.org/dev/peps/pep-0561/