Migrate to pyproject.toml & hatch

[anselor]

The default recommendation from python seems to be hatch now. It has impressive features including declaring build/test configurations and managing venv environments. In my trial of it on a couple small projects I found it to be much faster than using nox to set up venvs.

The problem is it currently doesn't support a monorepo project with multiple modules or plugin modules. There is a development ticket (https://github.com/pypa/hatch/issues/233) that documents it and it is under active development now. Once that is complete we should be able to migrate to hatch with minimal fuss.