telemetry: add cruise engagement state for desync debugging

Added brakePressed to cruise group, prev_cruise_button and
prev_main_button to buttons group in carstate telemetry. New "engage"
group in controlsd logs state machine state, enabled/active flags, and
stock cruise state every frame for tracing engagement desync bugs.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

selfdrive/car/hyundai/carstate.py

@@ -446,6 +446,7 @@ class CarState(CarStateBase):
       "speed": round(ret.cruiseState.speed, 3),
       "standstill": ret.cruiseState.standstill,
       "accFaulted": ret.accFaulted,
+      "brakePressed": ret.brakePressed,
       "ACCMode": scc.get("ACCMode", 0),
       "VSetDis": scc.get("VSetDis", 0),
       "aReqRaw": round(scc.get("aReqRaw", 0), 3),
@@ -468,7 +469,9 @@ class CarState(CarStateBase):
 
     tlog("buttons", {
       "cruise_button": self.cruise_buttons[-1],
+      "prev_cruise_button": self.prev_cruise_buttons,
       "main_button": self.main_buttons[-1],
+      "prev_main_button": self.prev_main_buttons,
       "lkas_enabled": self.lkas_enabled,
       "main_enabled": self.main_enabled,
     })