Improve Wikidata test resiliency with retries and backoff

[adulau]

Motivation

• Reduce flakiness of the Wikidata expansion test by retrying transient failures and avoiding immediate test failures when the Wikidata endpoint (or the local proxy) is temporarily unreachable or rate-limited.

Description

• Added an import of time and updated tests/test_expansions.py to implement a retry/backoff loop for test_wikidata with max_attempts = 4 and wait_seconds = 2.
• The new test_wikidata catches and retries on requests.exceptions.RequestException and treats specific server-side error messages as retryable before failing the test.
• Preserves the original acceptable outcomes ("http://www.wikidata.org/entity/Q95", "No additional data found on Wikidata", and the server error message) while reducing false negatives from transient network/API issues.

Testing

• Ran pytest -q tests/test_expansions.py -k test_wikidata in this environment, which failed due to the local service being unreachable (Connection refused to 127.0.0.1:6666), indicating the failure is environmental and not caused by the test logic changes.

---

Codex Task