fix: resolve volumes multiget endpoint failing with .json extension

[RsbhThakur]

Closes #13092

fix

Technical

• Removed the manual URL regex parsing code (MULTIGET_PATH_RE) in get_volumes_multiget (in openlibrary/fastapi/books.py). FastAPI/Starlette already parses the req parameter and automatically strips the .json extension from the URL.
• Bypassed the custom regex block to directly pass the pre-parsed req parameter to readlinks.readlinks(req, {}).
• Removed the unused import re and import urllib.parse at the top of books.py (cleaned up automatically via Ruff linter).
• Updated all three unit test methods under TestGetVolumesMultiget in openlibrary/tests/fastapi/test_books.py to assert the exact arguments passed to the mocked readlinks function, eliminating mock testing gaps and preventing future regressions.

Testing

1. Run the local development environment.
2. Verify the multiget volumes API works with the .json extension:

   curl -i http://localhost:8080/api/volumes/brief/json/oclc:19683037.json

   Expected: Returns the full metadata JSON block for the OCLC record.
   Actual (Before): Returned {} empty response.
3. Run unit tests inside the Docker container to ensure all mock assertions pass successfully:

   docker compose run --rm home pytest openlibrary/tests/fastapi/test_books.py

Screenshot

N/A (This is a backend API bug fix).

[openlibrary-bot]

Thanks for the PR, @RsbhThakur!

The linked issue hasn't been triaged yet — triage happens on Mondays and Fridays. There are currently 30 open non-draft PRs ahead of yours.

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