Fix pfs namespace across various repos

Most of our python code lives under the pfs namespace but we don't have the repos set up properly to utilize that namespace, which causes local install failures and mis-leading error messages in modern IDEs.

The namespace should be cleaned up with a proper usage of PEP 420, which should be specified via a pyproject.toml file. Most of our repos currently don't have a pyproject file so this will need to be added.

Note that this should ideally include a push to remove all relative imports from anything within the pfs namespace. The removal of relative imports should be done within a separate ticket although it might need to be coordinated with this ticket.