start
Start watching the Room for publications that match the target participant identity and/or track name. Calls onSubscribed when a subscribed Track instance is available for the matching publication.
The helper will also scan existing remote participants/publications immediately when started.
Parameters
LiveKit Room instance
CoroutineScope to launch the watcher in (e.g., viewModelScope)
optional participant.identity to match (null = any participant)
optional publication.name or trackSid to match (null = any track)
callback invoked with the concrete track object, the publisher and the publication
optional lambda that will be called for a matching publication when the SDK hasn't produced a Track instance yet (publication.track == null). Use this to perform any SDK-specific manual subscribe call. If null, the helper will not attempt manual subscription.