refactor(storage): remove Service.ts and migrate logic to StorageTransport (googleapis#8283)

- Remove Service.ts and common.ts files from handwritten/storage

- Migrate remaining functionality to StorageTransport

- chore(ci): upgrade conformance tests to Node 18

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