feat: ramp-up delay on lat engagement to prevent commIssue flash

Decouples "tell modeld to go fast" from "steering actually active":
- New LatRequested memory param — controlsd writes when lat would be active
- modeld reads LatRequested (not carControl.latActive) for FPS decision,
  so it switches to 20fps immediately on engage request
- controlsd delays CC.latActive becoming true by 250ms (5 frames @ 20fps)
  after LatRequested goes true, giving downstream services
  (longitudinalPlan, liveCalibration, etc.) time to stabilize at the new rate

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

selfdrive/modeld/modeld.py

@@ -242,10 +242,12 @@ def main(demo=False):
     sm.update(0)
 
     # CLEARPILOT: power saving — three modes based on driving state
-    #   Full 20fps: lat active or lane changing
-    #   Reduced 4fps: not lat active, not standstill (driving without cruise)
+    #   Full 20fps: lat requested or lane changing
+    #   Reduced 4fps: not lat requested, not standstill (driving without cruise)
     #   Standby 0fps: standstill
-    lat_active = sm['carControl'].latActive
+    # Uses LatRequested (not carControl.latActive) so modeld ramps to 20fps BEFORE
+    # controlsd actually engages steering — gives downstream services time to stabilize.
+    lat_active = params_memory.get_bool("LatRequested")
     lane_changing = params_memory.get_bool("no_lat_lane_change")
     standstill = sm['carState'].standstill
     calibrating = sm['liveCalibration'].calStatus != log.LiveCalibrationData.Status.calibrated