timed: publish clocks periodically (#31434)

* timed: publish clocks periodically

* simplify

* Apply suggestions from code review

cereal

@@ -1 +1 @@
-Subproject commit 9b573c2be34b638ff462648308d3c7075d0ff174
+Subproject commit e842020c1c7a2c43fda17f4075307ae8abb9bc3a

system/timed.py

@@ -65,10 +65,15 @@ def main() -> NoReturn:
     cloudlog.debug("Restoring timezone from param")
     set_timezone(tz)
 
+  pm = messaging.PubMaster(['clocks'])
   sm = messaging.SubMaster(['liveLocationKalman'])
   while True:
     sm.update(1000)
 
+    msg = messaging.new_message('clocks', valid=True)
+    msg.clocks.wallTimeNanos = time.time_ns()
+    pm.send('clocks', msg)
+
     llk = sm['liveLocationKalman']
     if not llk.gpsOK or (time.monotonic() - sm.logMonoTime['liveLocationKalman']/1e9) > 0.2:
       continue