feat: basic database functionality

lib/data/models/statistic.dart

@@ -1,8 +1,10 @@
 import 'package:tallee/core/enums.dart';
 import 'package:tallee/data/models/game.dart';
 import 'package:tallee/data/models/group.dart';
+import 'package:uuid/uuid.dart';
 
 class Statistic {
+  final String id;
   final StatisticType type;
   final List<StatisticScope> scopes;
   final Timeframe? timeframe;
@@ -12,8 +14,14 @@ class Statistic {
   Statistic({
     required this.type,
     required this.scopes,
+    String? id,
     this.timeframe,
     this.selectedGroups,
     this.selectedGames,
-  });
+  }) : id = id ?? const Uuid().v4();
+
+  @override
+  String toString() {
+    return 'Statistic(id: $id, type: $type, scopes: $scopes, timeframe: $timeframe, selectedGroups: $selectedGroups, selectedGames: $selectedGames)';
+  }
 }