Add type-hints

For anyone reviewing, the easiest way will be to look at per commit changes. I rebased and committed one package at a time.

I hacked in the updates to the requirements.txt/in files without a full regen, as I don't like the current setup. It is confusing and error-prone. I want to do another follow up MR where I go through and move the project to using a pyproject.toml and fully and specifying the deps as extras.

A set of generated pinned dependencies can be created for the common sets of extras combinations.