Expose updates from other connect devices when not active

[photovoltex]

Is your feature request related to a problem? Please describe.
When implementing librespot as client (mostly GUI related) and not being the active connect device, there isn't any option to update the client UI as the remote events/updates are not exposed.

Describe the solution you'd like
It would be nice to call a similar method like player_event_handler on the spirc instance to retrieve a channel that exposes remote updates. Additionally we could also provide some local updates that exposes internal knowledge like the current next and previous tracks for example.

Additional context

• remote updates are send as ClusterUpdate
  • https://github.com/librespot-org/librespot/blob/dev/connect/src/spirc.rs#L816
• updates to the remote server when we are active are send as PutStateRequest
  • https://github.com/librespot-org/librespot/blob/dev/connect/src/spirc.rs#L1525