feat: async ChonkVerify protocol with request IDs and C++ worker threads

[AztecBot]

Summary

Adds async verification support to the bb IPC protocol, allowing ChonkVerify jobs to run on dedicated worker threads in C++ while the main IPC loop continues processing other requests.

Protocol change: Requests can now optionally include a request_id as [request_id, Command] (2-element array). The server detects this vs the legacy [Command] format automatically. Async responses are sent as [request_id, CommandResponse] and routed by ID on the TS side.

C++ changes:

• IpcServer gains a thread-safe async response queue (enqueue_async_response) that worker threads push to, drained by the main loop between iterations
• api_msgpack.cpp detects ChonkVerify commands with request_id > 0 and spawns std::thread workers. Each worker gets its own thread-local parallel_for pool (already lazy-initialized per thread). Uses a local BBApiRequest to avoid racing on the global one.
• Worker threads call wakeup_all() after enqueuing results to minimize latency

TS changes:

• Both socket and SHM backends now support callAsync() which wraps requests with a request_id and routes responses via Map<number, callback> instead of FIFO
• Legacy call() still uses FIFO matching — fully backward compatible
• IMsgpackBackendAsync interface gains optional callAsync?() method

This is the transport-layer foundation for the adaptive verifier pool (PR #21190) to dispatch multiple concurrent verification jobs through a single bb process.

Relates to Linear A-576.

ClaudeBox log: http://ci.aztec-labs.com/dbfbacde59b33f03-2