[Feature]: Scope PR coverage to changed packages; move full-suite coverage to a nightly run

[0xNeshi]

What is the feature you would like to see?

We currently run a full test suite coverage report on every PR (see test.yml). What's the value of measuring e.g. math/core coverage on a PR that only touches contracts/access?

We should split the coverage job into 2:

1. Coverage only on packages "touched" by the PR runs on each PR -> measures the actual PR impact on a package's code coverage. Keeps current value, while making coverage job faster (thus cheaper $).
2. Full test suite coverage -> runs nightly/weekly on main, sanity check on the project-wide code coverage.