fix: ensure test isolation in storage tests

- Use unique keys for each test to prevent SharedPreferences state leakage
- Fix flaky tests that were failing due to shared state between test runs
- Tests now pass consistently in CI/CD environments

Author: dshukertjr

packages/supabase_flutter/test/storage_test.dart

@@ -8,14 +8,17 @@ void main() {
   group('Storage Tests', () {
     // SharedPreferencesLocalStorage Tests
     group('SharedPreferencesLocalStorage', () {
-      const persistSessionKey = 'test_persist_key';
       const testSessionValue = '{"key": "value"}';
 
       Future<SharedPreferencesLocalStorage> createFreshLocalStorage() async {
+        // Use a unique key for each test to ensure complete isolation
+        final uniqueKey = 'test_persist_key_${DateTime.now().microsecondsSinceEpoch}';
+        
         // Set up fresh shared preferences for each test
         SharedPreferences.setMockInitialValues({});
+        
         final localStorage = SharedPreferencesLocalStorage(
-          persistSessionKey: persistSessionKey,
+          persistSessionKey: uniqueKey,
         );
         await localStorage.initialize();
         return localStorage;