Initial attempt to merge internal_state with kmk_keyboard. Seems to work on Plank so far

fix formatting

Example of new "Extension"/plugin system, using LED

Cleanup of RGB code

staticmethod to proper, normal methods

Needs cleanup, but: migrate Leader to Extension API

remove useless self reurns

fix an AttributeError with Leader key removal

Checkpoint from the weekend: split as an Extension (not working or done yet)

wip

kmk/extensions/split.py

@@ -0,0 +1,103 @@
+import busio
+import gc
+
+from kmk.extensions import Extension
+from kmk.kmktime import sleep_ms
+from kmk.matrix import intify_coordinate
+
+
+class SplitType:
+    UART = 1
+    I2C = 2  # unused
+    ONEWIRE = 3  # unused
+    BLE = 4  # unused
+
+
+class Split(Extension):
+    def __init__(
+        self,
+        extra_data_pin=None,
+        offsets=(),
+        flip=False,
+        side=None,
+        stype=None,
+        master_left=True,
+        uart_flip=True,
+        uart_pin=None,
+        uart_timeout=20,
+    ):
+        self.extra_data_pin = extra_data_pin
+        self.split_offsets = offsets
+        self.split_flip = flip
+        self.split_side = side
+        self.split_type = stype
+        self.split_master_left = master_left
+        self._uart = None
+        self.uart_flip = uart_flip
+        self.uart_pin = uart_pin
+        self.uart_timeout = uart_timeout
+
+    def during_bootup(self, keyboard):
+        if self.split_type is not None:
+            try:
+                # Working around https://github.com/adafruit/circuitpython/issues/1769
+                keyboard._hid_helper_inst.create_report([]).send()
+                self._is_master = True
+
+                # Sleep 2s so master portion doesn't "appear" to boot quicker than
+                # dependent portions (which will take ~2s to time out on the HID send)
+                sleep_ms(2000)
+            except OSError:
+                self._is_master = False
+
+            if self.split_flip and not self._is_master:
+                keyboard.col_pins = list(reversed(self.col_pins))
+            if self.split_side == 'Left':
+                self.split_master_left = self._is_master
+            elif self.split_side == 'Right':
+                self.split_master_left = not self._is_master
+        else:
+            self._is_master = True
+
+        if self.uart_pin is not None:
+            if self._is_master:
+                self._uart = busio.UART(
+                    tx=None, rx=self.uart_pin, timeout=self.uart_timeout
+                )
+            else:
+                self._uart = busio.UART(
+                    tx=self.uart_pin, rx=None, timeout=self.uart_timeout
+                )
+
+        # Attempt to sanely guess a coord_mapping if one is not provided.
+        if not keyboard.coord_mapping:
+            keyboard.coord_mapping = []
+
+            rows_to_calc = len(keyboard.row_pins)
+            cols_to_calc = len(keyboard.col_pins)
+
+            if self.split_offsets:
+                rows_to_calc *= 2
+                cols_to_calc *= 2
+
+            for ridx in range(rows_to_calc):
+                for cidx in range(cols_to_calc):
+                    keyboard.coord_mapping.append(intify_coordinate(ridx, cidx))
+
+        gc.collect()
+
+    def before_matrix_scan(self, keyboard_state):
+        if self.split_type is not None and self._is_master:
+            return self._receive_from_slave()
+
+    def after_matrix_scan(self, keyboard_state, matrix_update):
+        if matrix_update is not None and not self._is_master:
+            self._send_to_master(matrix_update)
+
+    def _send_to_master(self, update):
+        if self.split_master_left:
+            update[1] += self.split_offsets[update[0]]
+        else:
+            update[1] -= self.split_offsets[update[0]]
+        if self._uart is not None:
+            self._uart.write(update)