Add decorators for determining keyboard and keymap based on current directory (#8191)

* Use pathlib everywhere we can

* Improvements based on @erovia's feedback

* rework qmk compile and qmk flash to use pathlib

* style

* Remove the subcommand_name argument from find_keyboard_keymap()

* add experimental decorators

* Create decorators for finding keyboard and keymap based on current directory.

Decorators were inspired by @Erovia's brilliant work on the proof of concept.

lib/python/qmk/cli/__init__.py

@@ -2,6 +2,8 @@
 
 We list each subcommand here explicitly because all the reliable ways of searching for modules are slow and delay startup.
 """
+from milc import cli
+
 from . import cformat
 from . import compile
 from . import config
@@ -16,3 +18,6 @@ from . import kle2json
 from . import new
 from . import pyformat
 from . import pytest
+
+if not hasattr(cli, 'config_source'):
+    cli.log.warning("Your QMK CLI is out of date. Please upgrade with `pip3 install --upgrade qmk` or by using your package manager.")