Session migration (#72)

* impl

* retry logic

* simulate

* pass checks

* adjust log level

* retry condition

* fix simulate scenario params

* format

* use `RTCPeerConnectionState` instead of `RTCIceConnectionState`

* adjust retry

* additional check for completer

* more logging

* fix id

* pub

* change package

* doc update

* retry tests

* format

* apply suggestions

lib/src/core/transport.dart

@@ -31,7 +31,7 @@ class PCTransport extends Disposable {
       // Ensure callbacks won't fire any more
       pc.onRenegotiationNeeded = null;
       pc.onIceCandidate = null;
-      pc.onIceConnectionState = null;
+      pc.onConnectionState = null;
       pc.onTrack = null;
 
       // Remove all senders