Code coverage improvements

[ana-pantilie]

As a Plutus Core developer I want to have code coverage reports so I know if I have tested my code adequately.

Acceptance criteria Coverage reports for our test suites are automatically generated

(Maybe?) CI is set up to fail if certain coverage metrics decrease

• [x] https://github.com/IntersectMBO/plutus/issues/6131
• [x] https://github.com/IntersectMBO/plutus/issues/6132
• [ ] https://github.com/IntersectMBO/plutus/issues/6133

[effectfully]

This now just refers to the single open issue, so we can as well only have that issue open and close this one.

[ana-pantilie]

Thank you for cleaning this up @effectfully !