Add temporary storage path for tests in EnsembleTestHarness

Introduce a static variable for a temporary storage path in the EnsembleTestHarness class, enhancing the test environment by directing certain method channel calls to this path instead of the current directory. This change improves test isolation and management of temporary files during test execution.

Author: sharjeelyunus

packages/ensemble_test_runner/lib/runner/ensemble_test_harness.dart

@@ -1,4 +1,5 @@
 import 'dart:async';
+import 'dart:io';
 
 import 'package:ensemble/ensemble.dart';
 import 'package:ensemble/ensemble_app.dart';
@@ -37,6 +38,9 @@ void applyYamlTestBootstrap(EnsembleConfig config, EnsembleTestSetup setup) {
 
 /// Boots the real Ensemble runtime for widget tests.
 class EnsembleTestHarness {
+  static final String _testStoragePath =
+      Directory.systemTemp.createTempSync('ensemble_test_runner_storage_').path;
+
   static void ensureTestPlugins() {
     TestWidgetsFlutterBinding.ensureInitialized();
     const pathProviderChannel =
@@ -47,7 +51,7 @@ class EnsembleTestHarness {
         case 'getApplicationDocumentsDirectory':
         case 'getTemporaryDirectory':
         case 'getApplicationSupportDirectory':
-          return '.';
+          return _testStoragePath;
         default:
           return null;
       }