github/workflows: Add job to upload coverage reports

- Updated `test-and-publish.yml` to include coverage report uploads
  for all tested Python versions.
- Stored coverage reports under `coverage/py<python-version>` for
  organized access and tracking.

Assisted-by: Codex

Author: datalogics-kam

.github/workflows/test-and-publish.yml

@@ -38,6 +38,12 @@ jobs:
         run: uvx nox --python ${{ matrix.python-version }} --session tests -- --no-parallel
         env:
           PDFREST_API_KEY: ${{ secrets.PDFREST_API_KEY }}
+      - name: Upload coverage reports
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: coverage-${{ matrix.python-version }}
+          path: coverage/py${{ matrix.python-version }}
 
   examples:
     name: Examples (Python ${{ matrix.python-version }})