[2.0] chore: annotational value examples schall be schema-compliant

our tests currently check that all `default` (and `enum`) values are schema-compliant. done in the tests.

missing: check examples

the check runs with a best-effort implementation, rather an actual schema checker.
this shall be changed:
- use an actual fully-fledged schema checker for these values
- also check examples

unclear: where to put this.
- maybe in the linter?
- maybe in the keep it in the tests?