feat: 10fps daytime / 4fps night modeld + 2Hz GPS

Reduced-rate modeld path now branches on IsDaylight:
- daylight: skip 1/2 frames → 10fps (better model responsiveness when
  lighting gives the net more signal)
- night: skip 4/5 frames → 4fps (unchanged, conservative for power)

IsDaylight is already in /dev/shm (memory) via gpsd.py. Gated the
IsDaylight write on change — it flips twice a day, no reason to rewrite
every 30s. GPS polling bumped from 1Hz → 2Hz.

ModelFps publishes "10" / "4" / "20" so longitudinal_planner's dt and
FCW-threshold scaling (if re-enabled) still track actual rate.

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

selfdrive/modeld/modeld.py

@@ -273,17 +273,21 @@ def main(demo=False):
       last_vipc_frame_id = meta_main.frame_id
       continue
 
-    # Reduced framerate: 4fps when not lat active and not standstill
-    # Skip 4 out of every 5 frames (20fps -> 4fps)
+    # Reduced framerate: daylight 10fps (skip 1/2), night 4fps (skip 4/5)
+    # Daytime runs twice as fast — better model responsiveness when lighting is good
+    # and the neural net has more signal. Night stays conservative for power.
     # Write standby timestamp so controlsd suppresses transient errors
     if not full_rate:
-      if params_memory.get("ModelFps") != b"4":
-        params_memory.put("ModelFps", "4")
+      is_daylight = params_memory.get_bool("IsDaylight")
+      skip_interval = 2 if is_daylight else 5
+      target_fps = b"10" if is_daylight else b"4"
+      if params_memory.get("ModelFps") != target_fps:
+        params_memory.put("ModelFps", target_fps.decode())
       now = _time.monotonic()
       if now - last_standby_ts_write > 1.0:
         params_memory.put("ModelStandbyTs", str(now))
         last_standby_ts_write = now
-      if run_count % 5 != 0:
+      if run_count % skip_interval != 0:
         last_vipc_frame_id = meta_main.frame_id
         run_count += 1
         continue