[CI/CD] Add test coverage reporting with Codecov

[stepmikhaylov]

Integrate Codecov into CI. This requires registering the repository with Codecov, storing the CODECOV_TOKEN in GitHub Actions secrets, and creating the workflow file that collects and uploads coverage on each PR.

Source: #513

[asclearuc]

Implemented for AI package by #831
Need to be implemented for nodes
It does not use codecov, the solution is based on the pytest itself with additional parameter --cov