Reconsider requirement file segmentation

[rsyring]

I thought it would make sense to have a CI reqs file but it turns out the CI setup is rather complicated due to the various layers involved in testing the demo & bootstrap tasks.

I had intended for mise and reqs to be the two tools installed at the system level. But installing reqs in CI didn't result in them getting on the path. So they ended up being installed in the mise venv as well as in the nox venv for the tests. Seems like it might be a path issue with the cimg/python image as python -m pip install <reqs url> doesn't result in reqs being on the path. Can work on that with #4.

[rsyring]

Also, for libraries, we aren't going to want to use frozen requirements or have test dependencies in the base requirements.