Enhance CI workflow with coverage reporting and README badges

[sni10]

This pull request adds comprehensive tests for the upload_to_stash and publish_deviation functions, improves test coverage reporting, and enhances project documentation with badges. The main improvements are grouped below.

Testing improvements:

• Added unit tests for upload_to_stash and publish_deviation using unittest.mock to simulate HTTP requests, covering success cases, API errors, network errors, and optional parameters.
• Imported the necessary functions and mocking utilities in tests/test_node.py to support the new tests. [1] [2]

CI and coverage reporting:

• Updated .github/workflows/ci.yml to install pytest-cov, run tests with coverage collection, and upload coverage reports to Codecov.

Documentation:

• Added status and coverage badges to README.md to display release version, test status, coverage, supported Python version, and license.