added methods for interacting with User, Group and UserGroup in database

lib/data/methods/group.dart

@@ -0,0 +1,28 @@
+import 'package:game_tracker/data/database.dart';
+import 'package:drift/drift.dart';
+
+extension Group on AppDatabase {
+  Future<List<GroupData>> getAllGroups() async {
+    return await select(group).get();
+  }
+
+  Future<List<GroupData>> getGroupById(String id) async {
+    return await (select(group)..where((g) => g.id.equals(id))).get();
+  }
+
+  Future<void> addGroup(String id, String name) async {
+    await into(group).insert(
+      GroupCompanion.insert(id: id, name: name),
+    );
+  }
+
+  Future<void> deleteGroup(String id) async {
+    await (delete(group)..where((u) => u.id.equals(id))).go();
+  }
+
+  Future<void> updateGroupname(String id, String newName) async {
+    await (update(group)..where((u) => u.id.equals(id))).write(
+      GroupCompanion(name: Value(newName)),
+    );
+  }
+}