Integrate Codecov for coverage report uploads

Add Codecov action to upload coverage reports.

Author: heptaflar

.github/workflows/python-package.yml

@@ -39,3 +39,9 @@ jobs:
     - name: Test with pytest
       run: |
         pytest --cov=.
+    - name: Upload coverage reports to Codecov
+      uses: codecov/codecov-action@v5
+      with:
+        token: ${{ secrets.CODECOV_TOKEN }}
+        slug: bcdev/uncertaintyx
+