fix(api): check HTTP status before decoding POST responses

[JianYan11]

Summary

Fixes #95.

Move response.raise_for_status() immediately after the Table API request, before the POST branch reads response.json()["result"]["sys_id"].

Previously, a failed POST with a JSON error body raised KeyError: 'result', and a failed POST with an HTML error page raised JSONDecodeError. Both masked the actual HTTP error. Successful POST polling and other method behavior are unchanged.

Tests

Added offline tests using real requests.Response objects, a lightweight instance stand-in, and mocked HTTP calls/sleep:

• JSON 401 and HTML 503 responses for GET, POST, PUT, and DELETE preserve the original HTTPError response, without decoding or polling.
• A successful POST still polls for its created sys_id and returns the original creation response.

Before the fix: 2 failed, 7 passed (the two POST error cases).
After the fix: 9 passed.

PYTHONPATH=src uv run --no-project --python 3.12 \
  --with-requirements requirements.txt --with 'playwright==1.44.0' --with pytest -- \
  python -m pytest tests/test_api_utils.py -q

Black 24.10.0 and git diff --check pass. No browser was launched, no ServiceNow instance was contacted, and the live-instance integration suite was not run.

AI assistance: implemented and tested with OpenAI Codex.