Add py.typed file to s3path for mypy support

[liormizr]

We are missing py.typed file, see https://mypy.readthedocs.io/en/stable/installed_packages.html#creating-pep-561-compatible-packages and https://peps.python.org/pep-0561/

mypy will ignore all typing information when that file is missing

I'm currently unavailable to work on this task. If someone wants to contribute this is a nice one.