add codecov to PR action

Author: paulbkoch

.github/workflows/pull_request.yml

@@ -39,4 +39,8 @@ jobs:
           pip install -e .[babytest]
       - name: Unit Tests
         run: |
-          pytest -vv ./tests/unit
+          python -m pytest ./tests/unit -vv --cov=guidance --cov-report=xml
+      - name: Upload coverage reports to Codecov
+        uses: codecov/codecov-action@v4
+        with:
+          token: ${{ secrets.CODECOV_TOKEN }}