firmware: auto-detect GPS UART baud

tests/test_xiao_sensor_node_contract.py

@@ -38,6 +38,12 @@ def test_imu_scans_both_bno08x_i2c_addresses():
     assert "findBnoAddress()" in imu
     assert "Wire.endTransmission()" in imu
 
+def test_gps_auto_detects_common_nmea_baud_rates():
+    gps = source("gps.cpp")
+    assert "baudHasValidNmea" in gps
+    assert "{9600, 38400, 115200, 4800}" in gps
+    assert "passedChecksum() > 0" in gps
+
 def test_node_does_not_take_cargo_or_ble_authority():
     combined = "\n".join(p.read_text() for p in NODE.glob("*.*"))
     assert "NimBLE" not in combined and "JBD" not in combined and "server.on(" not in combined