WIP - add github actions to run tests, linting, and some examples against various versions of python

[ukd1]

Not finished yet, but thought I'd open a draft PR. I've got to fix the skidl test, probably by skipping it for 3.12 unless I can figure out how to fix it, or get them to upstream it for 3.12 - doesn't seem to be anything in the existing code here btw.