Add test result artifact uploads to CI workflow

- Upload coverage.xml and htmlcov/ as artifacts after test runs
- Artifacts available for download from GitHub Actions UI
- Retained for 30 days for debugging and coverage analysis
- Makes HTML coverage reports accessible from CI runs

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: ritwik-g

.github/workflows/ci.yml

@@ -59,6 +59,16 @@ jobs:
         flags: unittests
         name: codecov-umbrella
 
+    - name: Upload test results
+      if: always()
+      uses: actions/upload-artifact@v4
+      with:
+        name: test-results-${{ matrix.os }}-py${{ matrix.python-version }}
+        path: |
+          coverage.xml
+          htmlcov/
+        retention-days: 30
+
   lint:
     runs-on: ubuntu-latest
     steps: