Feature: Test contributing tasks in the CI

[vjovanov]

Is your feature request related to a problem?

This is currently not done and makes contributing fragile.

Describe the solution you'd like

Simply test:

./gradlew scaffold --coordinates com.example:my-library:1.0.0

And then check the new library scaffold:

./gradlew testInfra -Pcoordinates=com.example:my-library:1.0.0

If something is missing, we can add it to scaffold or manually (e.g., reachability-metadata.json)

Describe alternatives you've considered

No response

Additional context

No response