Convert klippy to a python package

[kageurufu]

1. Fix all imports within klippy to be relative, or absolute klippy.mod

2. For compatibility with external extras that will probably still use the old import names (e.g. a bare import stepper instead of from klippy import stepper), klippy/compat.py hot patches sys.modules before starting the Printer reactor. Any module currently in sys.modules under the klippy. package namespace are inserted a second time with the leading namespace stripped.

   • To keep compatibility with klippy.xxx being used, klippy/__init__.py does from klippy.printer import *, ensuring all legacy values exist

3. For compatibility with running python klippy/klippy.py (every current printer's systemd service, as well as any KIAUH install), a shim klippy/klippy.py is in place that patches sys.path before importing and calling klippy.printer.main()

Checklist

• pr title makes sense
• squashed to 1 commit
• added a test case if possible
  • the existing ci-build.sh verifies python klippy/klippy.py still works, and scripts/test-klippy.py uses the new python -m klippy
• if new feature, added to the readme
• ci is happy and green

[kageurufu]

I feel like this works, its ready.

We need to validate more extras than just Beacon and Shaketune, but those work.