* Add `WakeLock` to dismiss ringing call screen when call is cancelled
We had already some checks in place to automatically cancel a ringing call notification/screen when the call was no longer active, but the `RoomInfo` updates weren't being processed because the app was 'paused'.
The partial wakelock should ensure these room info updates are handled.
* Add mutual exclusion to `ActiveCallManager` methods to improve thread safety
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