Continue to shuffle and burn stuff

- Remove the concept of "mcus". With only one target platform
(CircuitPython), it no longer makes a bunch of sense and has been kept
around for "what if" reasons, complicating our import chains and eating
up RAM for pointless subclasses. If you're a `board`, you derive from
`KeyboardConfig`. If you're a handwire, the user will derive from
`KeyboardConfig`. The end. As part of this, `kmk.hid` was refactored
heavily to emphasize that CircuitPython is our only supported HID stack,
with stubs for future HID implementations (`USB_HID` becomes
`AbstractHID`, probably only usable for testing purposes,
`CircuitPython_USB_HID` becomes `USBHID`, and `BLEHID` is added with an
immediate `NotImplementedError` on instantiation)

- `KeyboardConfig` can now take a HID type at runtime. The NRF52840
boards will happily run in either configuration once CircuitPython
support is in place, and a completely separate `mcu` subclass for each
mode made no sense. This also potentially allows runtime *swaps* of HID
driver down the line, but no code has been added to this effect. The
default, and only functional value, for this is `HIDModes.USB`

- Most consts have been moved to more logical homes - often, the main
or, often only, component that uses them. `DiodeOrientation` moved to
`kmk.matrix`, and anything HID-related moved to `kmk.hid`

user_keymaps/kdb424/gherkin.py

@@ -1,9 +1,10 @@
 import board
 
-from kmk.consts import DiodeOrientation, UnicodeMode
+from kmk.consts import UnicodeMode
 from kmk.handlers.sequences import compile_unicode_string_sequences, send_string
 from kmk.keys import KC
-from kmk.mcus.circuitpython_usbhid import KeyboardConfig
+from kmk.matrix import DiodeOrientation
+from kmk.keyboard_config import KeyboardConfig
 from kmk.types import AttrDict
 
 keyboard = KeyboardConfig()

user_keymaps/kdb424/klanck.py

@@ -1,9 +1,10 @@
 import board
 
-from kmk.consts import DiodeOrientation, UnicodeMode
+from kmk.consts import UnicodeMode
 from kmk.handlers.sequences import compile_unicode_string_sequences, send_string
 from kmk.keys import KC
-from kmk.mcus.circuitpython_usbhid import KeyboardConfig
+from kmk.matrix import DiodeOrientation
+from kmk.keyboard_config import KeyboardConfig
 from kmk.types import AttrDict
 
 keyboard = KeyboardConfig()