Offload functions to worker threads with shared memory primitives for Node.js.

feat: pipeline example and process exit verification master

Fix worker ref/unref lifecycle so dedicated workers don't hold the event loop open when idle: setupWorker before unref (so unref wins), then ref/unref around each execute() call and for the duration of each dispatchStream(). Streaming port1 is unref'd after its listener is added, so stream completion triggers natural exit. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>