Fully type module then mark as `py.typed`

This is an issue to track `jaraco.develop` being marked as `py.typed`.
I'd rather not lie about the typed state of a library and wait until all its public members are fully annotated (or at least to a "best effort") before being marked as `py.typed`.

Refs:
- https://github.com/jaraco/skeleton/issues/98
- https://github.com/jaraco/skeleton/pull/136#discussion_r1714057809
- https://github.com/pypa/setuptools/issues/2345

No files, tests, or entry points are identified in the issue. Begin by inventorying jaraco.develop's public members and determining the current annotation coverage; completion means the public API is fully or best-effort typed and the package can be marked py.typed without misrepresenting its typed state.

Written by the indexing model from the issue text.