added prototype of GameRound model

lib/pangea/pages/games/story_game/round_model.dart

@@ -0,0 +1,28 @@
+import 'dart:async';
+
+enum RoundState { notStarted, inProgress, completed }
+
+class GameRoundModel {
+  static const Duration roundLength = Duration(minutes: 3);
+
+  Timer? timer;
+  DateTime? startTime;
+  DateTime? endTime;
+  RoundState state = RoundState.notStarted;
+
+  GameRoundModel() {
+    timer = Timer(roundLength, () => endRound());
+    startTime = DateTime.now();
+  }
+
+  void startRound() {
+    state = RoundState.inProgress;
+    startTime = DateTime.now();
+    timer = Timer(roundLength, () => endRound());
+  }
+
+  void endRound() {
+    endTime = DateTime.now();
+    state = RoundState.completed;
+  }
+}