Fix Codecov code coverage analysis from test data (#1434)

This PR does a few things in pursuit of fixing our integrated code coverage analysis provided by Codecov:

It removes the last usage of invoke from our GitHub Actions CI scripts. Now we rely purely on uv for everything.
Uploading of data to Codecov is now done using a private token which is stored in GitHub secrets for this repo.
Both test data and code coverage are now uploaded.

Author: tleonhardt

.github/workflows/tests.yml

@@ -36,11 +36,24 @@ jobs:
         run: uv sync --all-extras --dev
 
       - name: Run tests
-        run: uv run inv pytest --junit --no-pty --base
+        run: uv run python -m pytest --cov --cov-config=pyproject.toml --cov-report=xml tests
 
       - name: Run isolated tests
-        run: uv run inv pytest --junit --no-pty --isolated
+        run: uv run python -m pytest --cov --cov-config=pyproject.toml --cov-report=xml tests_isolated
 
-      - name: Upload coverage reports to Codecov with GitHub Action on Python 3.13 for each OS
+      - name: Upload test results to Codecov
+        if: ${{ !cancelled() }}
+        uses: codecov/test-results-action@v1
+        with:
+          flags: python${{ matrix.python-version }}
+          name: codecov-umbrella-test-results
+          token: ${{ secrets.CODECOV_TOKEN }}
+      - name: Upload coverage to Codecov
         uses: codecov/codecov-action@v5
-        if: ${{ matrix.python-version == '3.13' }}
+        with:
+          env_vars: OS,PYTHON
+          fail_ci_if_error: true
+          flags: unittests
+          name: codecov-umbrella
+          token: ${{ secrets.CODECOV_TOKEN }}
+          verbose: true