fix: some fixes in example app

lib/tools/history.dart

@@ -11,8 +11,7 @@ Future<List<GymHistoryItem>> getHistory() async {
   for (var historyItem in jsonDecode(historyString) as List<dynamic>) {
     history.add(GymHistoryItem.fromJson(historyItem));
   }
-  history.sort((a, b) => b.id.compareTo(a.id));
-  history = history.reversed.toList();
+  history.sort((a, b) => b.timestamp.compareTo(a.timestamp));
   return history;
 }
 
@@ -50,7 +49,8 @@ Future<void> addToHistory(GymHistoryItemDetail item) async {
     "receiver": item.receiver,
     "email": item.email,
     "address": item.address,
-    "providers": providers
+    "providers": providers,
+    "timestamp": DateTime.now().millisecondsSinceEpoch.toString(),
   };
   final detailHistoryItem = GymHistoryItemDetail.fromJson(json);
   detailHistory.add(detailHistoryItem);
@@ -59,6 +59,7 @@ Future<void> addToHistory(GymHistoryItemDetail item) async {
     id: detailHistoryItem.id,
     photo: detailHistoryItem.providers[0].items[0].photo,
     sum: detailHistoryItem.sum,
+    timestamp: detailHistoryItem.timestamp,
   ));
   prefs.setString('history', jsonEncode(history));
   prefs.setString('detail_history', jsonEncode(detailHistory));