Add codecov for unit test coverage

Author: varshaprasad96

.github/workflows/unit-tests.yml

@@ -29,3 +29,7 @@ jobs:
           coverage run -m --source=src pytest -v tests/unit_test.py
           coverage=$(coverage report -m | tail -1 | tail -c 4 | head -c 2)
           if (( $coverage < 90 )); then echo "Coverage failed at ${coverage}%"; exit 1; else echo "Coverage passed, ${coverage}%"; fi
+      - name: Upload to Codecov
+        uses: codecov/codecov-action@v3
+        with:
+          token: ${{ secrets.CODECOV_TOKEN }}