Fix/timestamp type error in ping pong (#173)

* fix: timestamp type error in ping/pong.

* Improve pub analyzer score.

lib/src/core/engine.dart

@@ -88,7 +88,7 @@ class Engine extends Disposable with EventsEmittable<EngineEvent> {
             peerConnectionCreate ?? rtc.createPeerConnection {
     if (kDebugMode) {
       // log all EngineEvents
-      events.listen((event) => logger.fine('[EngineEvent] $objectId ${event}'));
+      events.listen((event) => logger.fine('[EngineEvent] $objectId $event'));
     }
 
     _setUpEngineListeners();
@@ -156,7 +156,7 @@ class Engine extends Disposable with EventsEmittable<EngineEvent> {
 
   // resets internal state to a re-usable state
   Future<void> cleanUp() async {
-    logger.fine('[${objectId}] cleanUp()');
+    logger.fine('[$objectId] cleanUp()');
 
     await publisher?.dispose();
     publisher = null;

lib/src/core/signal_client.dart

@@ -261,7 +261,7 @@ class SignalClient extends Disposable with EventsEmittable<SignalEvent> {
 
   void _sendPing() {
     _sendRequest(lk_rtc.SignalRequest()
-      ..ping = DateTime.now().millisecondsSinceEpoch as Int64);
+      ..ping = Int64(DateTime.now().millisecondsSinceEpoch));
   }
 
   void _startPingInterval() {
@@ -274,7 +274,7 @@ class SignalClient extends Disposable with EventsEmittable<SignalEvent> {
     }
 
     _pingIntervalTimer ??=
-        Timer.periodic(_pingIntervalDuration!, (_) => _sendPing);
+        Timer.periodic(_pingIntervalDuration!, (_) => _sendPing());
   }
 
   void _clearPingInterval() {