Feature: Full-Duplex Wired Split (#2766)

refactor(split): Refactor split code for extension

Extract central/peripheral code to allow for plugging in alternate
transports, instead of tying all split logic to BT.

feat(split): Add full-duplex wired split support

* Depends on full-duplex hardware UART for communication.
* Supports all existing central commands/peripheral events, including
  sensors/inputs from peripherals.
* Only one wired split peripheral supported (for now)
* Relies on chosen `zmk,split-uart` referencing the UART device.

docs: Add wired split config docs.

Migrate split to its own dedicated config file, and add details
on wired split config.

Co-authored-by: Nicolas Munnich <98408764+Nick-Munnich@users.noreply.github.com>

fix: Properly override stack size on RP2040

Move the system work queue stack size override on RP2040 ouf of
a `ZMK_BLE` conditional so it is properly applied generally for that
SoC.

---------

Co-authored-by: Nicolas Munnich <98408764+Nick-Munnich@users.noreply.github.com>

app/src/split/Kconfig

@@ -9,16 +9,20 @@ if ZMK_SPLIT
 config ZMK_SPLIT_ROLE_CENTRAL
     bool "Split central device"
 
-choice ZMK_SPLIT_TRANSPORT
-    prompt "Split transport"
-
 config ZMK_SPLIT_BLE
-    bool "BLE"
+    bool "BLE Split"
+    default y
     depends on ZMK_BLE
     select BT_USER_PHY_UPDATE
     select BT_AUTO_PHY_UPDATE
 
-endchoice
+config ZMK_SPLIT_WIRED
+    bool "Wired Split"
+    default y if !ZMK_SPLIT_BLE
+    depends on DT_HAS_ZMK_WIRED_SPLIT_ENABLED
+    select SERIAL
+    select RING_BUFFER
+    select CRC
 
 config ZMK_SPLIT_PERIPHERAL_HID_INDICATORS
     bool "Peripheral HID Indicators"
@@ -29,3 +33,4 @@ config ZMK_SPLIT_PERIPHERAL_HID_INDICATORS
 endif # ZMK_SPLIT
 
 rsource "bluetooth/Kconfig"
+rsource "wired/Kconfig"