[client, relay-server] Feature/relay notification (#4083)

- Clients now subscribe to peer status changes.
- The server manages and maintains these subscriptions.
- Replaced raw string peer IDs with a custom peer ID type for better type safety and clarity.

client/internal/peer/conn.go

@@ -167,7 +167,7 @@ func (conn *Conn) Open(engineCtx context.Context) error {
 
 	conn.ctx, conn.ctxCancel = context.WithCancel(engineCtx)
 
-	conn.workerRelay = NewWorkerRelay(conn.Log, isController(conn.config), conn.config, conn, conn.relayManager, conn.dumpState)
+	conn.workerRelay = NewWorkerRelay(conn.ctx, conn.Log, isController(conn.config), conn.config, conn, conn.relayManager, conn.dumpState)
 
 	relayIsSupportedLocally := conn.workerRelay.RelayIsSupportedLocally()
 	workerICE, err := NewWorkerICE(conn.ctx, conn.Log, conn.config, conn, conn.signaler, conn.iFaceDiscover, conn.statusRecorder, relayIsSupportedLocally)
@@ -489,6 +489,8 @@ func (conn *Conn) onRelayConnectionIsReady(rci RelayConnInfo) {
 		conn.Log.Errorf("failed to add relayed net.Conn to local proxy: %v", err)
 		return
 	}
+	wgProxy.SetDisconnectListener(conn.onRelayDisconnected)
+
 	conn.dumpState.NewLocalProxy()
 
 	conn.Log.Infof("created new wgProxy for relay connection: %s", wgProxy.EndpointAddr().String())