Fix reseting the timer while it is being waited on

If the timer was reset while it was being waited on, the next tick time
was not recalculated and the timer would wait for the original time
instead of the new one.

Signed-off-by: Leandro Lucarella <[email protected]>

Author: llucax

src/frequenz/channels/timer.py

@@ -696,10 +696,15 @@ async def ready(self) -> bool:  # noqa: DOC502
 
         now = self._now()
         time_to_next_tick = self._next_tick_time - now
+
         # If we didn't reach the tick yet, sleep until we do.
-        if time_to_next_tick > 0:
+        # We need to do this in a loop also reacting to the reset event, as the timer
+        # could be reset while we are sleeping, in which case we need to recalculated
+        # the time to the next tick and try again.
+        while time_to_next_tick > 0:
             await asyncio.sleep(time_to_next_tick / 1_000_000)
             now = self._now()
+            time_to_next_tick = self._next_tick_time - now
 
         # If a stop was explicitly requested during the sleep, we bail out.
         if self._stopped: