add destructor test

thermion_dart/test/destructor_tests.dart

@@ -0,0 +1,18 @@
+import 'package:test/test.dart';
+import 'package:thermion_dart/src/viewer/src/ffi/src/ffi_filament_app.dart';
+import 'package:thermion_dart/src/viewer/viewer.dart';
+import 'helpers.dart';
+
+void main() async {
+  final testHelper = TestHelper("app");
+  
+
+  test('destroy app', () async {
+    await testHelper.setup();
+    final viewer = await testHelper.createViewer();
+    await viewer.dispose();
+    await FilamentApp.instance!.destroy();
+    await testHelper.setup();
+
+  });
+}