Fix memory leak in the timer

We were creating two futures, but only awaiting until the one of them
finished and not canceling the second.

Because `reset()` was never called, we were just creating more and
more futures that would never complete.

This change fixes this by canceling the second task immediately after
the first one is complete.

Signed-off-by: Sahas Subramanian <[email protected]>

Author: shsms

src/frequenz/channels/timer.py

@@ -682,14 +682,20 @@ async def ready(self) -> bool:  # noqa: DOC502
         # could be reset while we are sleeping, in which case we need to recalculate
         # the time to the next tick and try again.
         while time_to_next_tick > 0:
-            await next(
-                asyncio.as_completed(
-                    [
-                        asyncio.sleep(time_to_next_tick / 1_000_000),
-                        self._reset_event.wait(),
-                    ]
-                )
+            _, pending = await asyncio.wait(
+                [
+                    asyncio.create_task(asyncio.sleep(time_to_next_tick / 1_000_000)),
+                    asyncio.create_task(self._reset_event.wait()),
+                ],
+                return_when=asyncio.FIRST_COMPLETED,
             )
+            for task in pending:
+                task.cancel()
+                try:
+                    await task
+                except asyncio.CancelledError:
+                    pass
+
             self._reset_event.clear()
             now = self._now()
             time_to_next_tick = self._next_tick_time - now