feature(#315): Support python 3.10+
Revamp CI workflow, condense files and jobs down, using matrices where
possible. Main idea: test with {earliest python+OS version, latest python+OS
version}, and assume that if those work then everything in between will work
too.
- Fix subtle nasty bug with pipeline where a nested usage of the
actions/checkout@v3 action caused inner the publish job always to run against
the master branch.
- Fix issue in upload-artifact excluding dotfiles by default (who introduces
breaking changes without major version increment???).
- Add caching for {homebrew, apt} packages and build files to try to get the
pipeline execution time down.
