fix(storage): resolve system test failures after Gaxios & Node 18 migration

- Updated StorageTransport to properly handle Gaxios interceptors.
- Resolved type mismatches in response handlers for Node 18.
- Fixed surgical restore logic in system-tests.

Author: thiyaguk09

.github/workflows/conformance-test.yaml

@@ -15,7 +15,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: actions/setup-node@v6
         with:
-          node-version: 14
+          node-version: 18
       - run: node --version
       - run: cd handwritten/storage && npm install
       - run: cd handwritten/storage && npm run conformance-test