Replace JS worker's rendezvous channel with unbounded queue

[joshua-spacetime]

Description of Changes

Previously, a module’s JS worker thread was fed through a zero-capacity channel. That made every request handoff a rendezvous between the async producer task and the single JS worker thread. Under high concurrency, that synchronous handoff showed up as hot flume/lock/wakeup stacks on the critical path - the JS worker thread.

This patch brings V8 execution in line with WASM which also uses an unbounded request queue.

Changing that handoff to an unbounded queue decouples request producers from the JS worker. Producers can enqueue work without synchronizing directly with the worker on every request, and the worker can continue draining queued requests without paying the rendezvous cost each time. This shortens the critical path, reduces scheduler/locking overhead and increases throughput.

API and ABI breaking changes

None

Expected complexity level and risk

2

Testing

Manual performance testing