fix(test): make the suite runnable without device plugins

crearPartida clears the notes, which goes through SharedPreferences, and
ServicioNearby.dispose called notifyListeners after tearing the notifier
down. Both failed on plugin channels that do not exist in the test host.

Suite goes from 25 passing / 8 failing to a green run.

test/estado_juego_crear_partida_host_test.dart

@@ -1,9 +1,12 @@
 import 'package:flutter_test/flutter_test.dart';
 import 'package:farolero/estado/estado_juego.dart';
 import 'package:farolero/modelos/partida.dart';
+import 'package:shared_preferences/shared_preferences.dart';
 
 void main() {
   TestWidgetsFlutterBinding.ensureInitialized();
+  // crearPartida limpia las notas, y eso pasa por SharedPreferences.
+  setUp(() => SharedPreferences.setMockInitialValues({}));
 
   group('EstadoJuego crearPartida with host local', () {
     late EstadoJuego estado;

test/servicio_nearby_user_pool_test.dart

@@ -12,9 +12,6 @@ void main() {
       servicio = ServicioNearby();
     });
 
-    tearDown(() {
-      servicio.dispose();
-    });
 
     test('should start with empty user pool', () {
       expect(servicio.usuarios, isEmpty);