more docs & clean up

lib/src/internal/types.dart

@@ -1,18 +1,32 @@
-
 import 'dart:ui';
 
 import 'package:meta/meta.dart';
 
 @internal
+@immutable
 class RendererVisibility {
   final String rendererId;
   final String trackId;
   final bool visible;
   final Size size;
-  RendererVisibility({
+  const RendererVisibility({
     required this.rendererId,
     required this.trackId,
     required this.visible,
     required this.size,
   });
-}
+}
+
+@internal
+@immutable
+class RTCOfferOptions {
+  final bool iceRestart;
+
+  const RTCOfferOptions({
+    this.iceRestart = false,
+  });
+
+  Map<String, dynamic> toMap() => <String, dynamic>{
+        if (iceRestart) 'iceRestart': true,
+      };
+}