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

lib/data/methods/user.dart

@@ -0,0 +1,28 @@
+import 'package:game_tracker/data/database.dart';
+import 'package:drift/drift.dart';
+
+extension User on AppDatabase {
+  Future<List<UserData>> getAllUsers() async {
+    return await select(user).get();
+  }
+
+  Future<List<UserData>> getUserById(String id) async {
+    return await (select(user)..where((u) => u.id.equals(id))).get();
+  }
+
+  Future<void> addUser(String id, String name) async {
+    await into(user).insert(
+      UserCompanion.insert(id: id, name: name),
+    );
+  }
+
+  Future<void> deleteUser(String id) async {
+    await (delete(user)..where((u) => u.id.equals(id))).go();
+  }
+
+  Future<void> updateUsername(String id, String newName) async {
+    await (update(user)..where((u) => u.id.equals(id))).write(
+      UserCompanion(name: Value(newName)),
+    );
+  }
+}