Add type maker to the library

[ssbarnea]

Related: #191
Related: https://peps.python.org/pep-0561/

[nicoddemus]

The PR is good, but given we use setuptools-scm, shouldn't we just drop MANIFEST.in altogether, since setuptools-scm by default will add all git-tracked files to the package by default?

cc @RonnyPfannschmidt

[bluetech]

I think the library is not ready for exposing the types yet. It would at least require an audit of types that are (transitively) reachable through the public API, and then documenting and exporting them properly, as they become "official" public API. Something similar to pytest-dev/pytest#7469.

[Tatsh]

I think the library is not ready for exposing the types yet. It would at least require an audit of types that are (transitively) reachable through the public API, and then documenting and exporting them properly, as they become "official" public API. Something similar to pytest-dev/pytest#7469.

I do not understand this position. Without py.typed in this project, @pytest.hookimpl cannot be seen as typed by Mypy. This is not covered by pytest-dev/pytest#7469.

[bluetech]

See #428