test(queue): remove real waits from the startup flush test

The startup flush test slept 1.24 s, mostly three 400 ms windows that
must outlast the 350 ms persistence debounce. The body now runs in
VirtualTime, so those waits and the debounce timer advance on virtual
time while platform-channel replies stay real. No production change;
the test body and assertions are unchanged.

test/download_queue_startup_flush_test.dart

@@ -13,6 +13,7 @@ import 'package:spotiflac_android/providers/settings_provider.dart';
 import 'package:spotiflac_android/services/app_state_database.dart';
 
 import 'support/fixed_settings.dart';
+import 'support/virtual_time.dart';
 
 const _earlyTrack = Track(
   id: 'example:early',
@@ -24,9 +25,11 @@ const _earlyTrack = Track(
 
 void main() {
   TestWidgetsFlutterBinding.ensureInitialized();
+  // The waits run on virtual time, including the 350 ms persistence debounce
+  // they must outlast.
   test(
     'startup restores, merges and retries only complete owned snapshots',
-    () async {
+    () => VirtualTime().run(() async {
       SharedPreferences.setMockInitialValues({
         'app_state_migrated_queue_to_sqlite_v1': true,
         'download_queue_user_paused_v1': true,
@@ -407,6 +410,6 @@ void main() {
       expect([writes, deletes], [7, 0]);
       explicitRetry.dispose();
       await (await AppStateDatabase.instance.database).close();
-    },
+    }),
   );
 }