Report and publish code coverage

[uniqueg]

Is your feature request related to a problem? Please describe.

Show code coverage of unit tests in project documentation and ensure that
code coverage does not drop between commits.

Describe the solution you'd like

Use CodeCov to analyze and publish code coverage.
Add a badge to the project's README.md. Set up CI integration and ensure
code coverage does not drop with proposed code changes.

Describe alternatives you've considered

N/A

Additional context

See here for an example that uses code coverage with CodeCov:

• ZARP-cli