Testing: split ble encoder test (#2754)

test(sensors): Add mock encoder sensor

Add a new mock sensor driver for generating mock encoder sensor channel
data.

test(split): Add a peripheral sensor split test

Test BLE split logic for peripheral sensors (encoders).

app/module/drivers/sensor/encoder_mock/Kconfig

@@ -0,0 +1,7 @@
+# Copyright (c) 2024 The ZMK Contributors
+# SPDX-License-Identifier: MIT
+
+config ZMK_SENSOR_ENCODER_MOCK
+    bool "Mock Encoder Sensor"
+    default y
+    depends on DT_HAS_ZMK_SENSOR_ENCODER_MOCK_ENABLED