Make ChessAppRouter a class.

lib/chess/chess_app.dart

@@ -14,8 +14,10 @@ class ChessApp extends StatelessWidget {
       child: BlocProvider(
         create: (_) => ChessBloc.getInstance(),
         child: MaterialApp.router(
-          theme: ThemeData.dark(useMaterial3: true),
-          routerConfig: router,
+          theme: ThemeData.dark(
+            useMaterial3: true,
+          ),
+          routerConfig: ChessAppRouter.getInstance().router,
           title: 'mChess v0.1.1337',
         ),
       ),

lib/utils/chess_router.dart

@@ -2,15 +2,25 @@ import 'package:go_router/go_router.dart';
 import 'package:mchess/pages/chess_game.dart';
 import 'package:mchess/pages/lobby_selector.dart';
 
-final router = GoRouter(
-  routes: [
-    GoRoute(
-      path: '/',
-      builder: (context, state) => const LobbySelector(),
-    ),
-    GoRoute(
-      path: '/play',
-      builder: (context, state) => const ChessGame(),
-    )
-  ],
-);
+class ChessAppRouter {
+  static final ChessAppRouter _instance = ChessAppRouter._internal();
+
+  ChessAppRouter._internal();
+
+  static ChessAppRouter getInstance() {
+    return _instance;
+  }
+
+  final router = GoRouter(
+    routes: [
+      GoRoute(
+        path: '/',
+        builder: (context, state) => const LobbySelector(),
+      ),
+      GoRoute(
+        path: '/play',
+        builder: (context, state) => const ChessGame(),
+      )
+    ],
+  );
+}