title: Does Timer.periodic need to be cancelled on widget unmount?
body: <p>I'm using flutter hooks, and using the Timer.periodic to do some processing in my widget.</p>
  <p>Here's how I'm using it:</p>
  <pre><code>    final countdownStream = useMemoized(
        () =&gt; Timer.periodic(
          // ...
        ),
      );
  </code></pre>
  <p>Do I need to cancel this or will it automatically be removed? If I extract the Timer.periodic to a reusable function, what then?</p>
  <p>Thanks</p>