gstplayer: Unschedule the clock when paused
When the player is paused, the clock "wait" times out and causes a high cpu usage. This issue is fixed by unscheduling the clock id when going the player is paused and then re-schedule it once the player resumes.
See https://gitlab.freedesktop.org/gstreamer/gstreamer/-/issues/673
Related: #443 (closed)