Monitor::Poll() ended by sleeping until 10 s after it started, and
PollThread::Stop() joins the thread, so Monitor::Close() waited for the
rest of that sleep: up to 10 s on every stop, reconnect and reload of a
zmc whose monitor has an ONVIF event listener, Janus, RTSP2Web, Go2RTC
or the Amcrest API enabled.
Wait for the next poll in PollThread::Run() on a condition variable
that Stop() notifies. Polls still start every 10 s.
fixes#5269
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
