Enable test coverage

[tatiana]

Description

To improve the testing health of the project, we will add a codecov integration s.t. all PRs with passing tests will recieve a codecov report. We will also fail any PR where code coverage goes down more than 2%.

Acceptance criteria

• Users should have the ability to locally run a code coverage plugin to get reports without submitting to CI
• CI should automatically generate a code coverage report when users submit a PR with passing tests
• As part of the pull request, evaluate the coverage and fail if the coverage goes down by more than -2%
• Enable code-cov on the Github repo