embedding-worker.js Bun probe

Trap: running embedding-worker.js in Node while injecting Bun-like globals looks like Bun coverage because the Bun branch is selected, but Node still supplies different module, loader, and worker semantics. Fix: execute the emitted Bun worker under Bun for artifact validation; keep separate Node Worker coverage for CJS. Unsupported-host test branches must report an explicit skip rather than silently return.