Sleep unused onboard SX1262 in RAK13302 builds

Adapt the optional onboard-radio probe for RAK3401 and RAK4631 cores using the external RAK13302 image. Preserve SPI1 radio ownership, external FEM startup, and ordinary RAK4631 primary-radio operation.

Probe before boot voltage protection, bound missing-chip waits, release temporary pads, and confirm cold sleep without waking the chip. Add sanitizer-backed host regression tests and CI coverage.

.github/workflows/run-unit-tests.yml

@@ -610,6 +610,7 @@ jobs:
           python3 -B test/test_gps_sync_preferences.py -v
           python3 -B test/test_rak_gps_power.py -v
           python3 -B test/test_rak_shutdown_power.py -v
+          python3 -B test/test_rak3401_onboard_radio.py -v
           python3 -B test/test_xiao_battery_safety.py -v
           python3 -B test/test_peripheral_mode_prefs.py -v
           python3 -B test/test_t1000e_sensor_power.py -v