fix(code): align Node.js engines with worker compatibility #133

packages/code declares engines: >=20.11, but its worker test suite fails on Node 22 (47 failures) and passes on Node 24.16.0, as documented while adding the CI job in #110.

Either make the worker implementation/tests compatible with the declared range or narrow the engines constraint so supported runtimes match verified behavior. Add CI coverage for the chosen supported versions.