Switch RPC transport from JSON-RPC to CBOR
- Update lib/worker.ml to use Transport.Cbor for encoding/decoding
- Update idl/js_top_worker_client.ml to use CBOR transport
- Update idl/js_top_worker_client_fut.ml to use CBOR transport
- Update example/unix_worker.ml to use CBOR and fix partial read issue
- Update example/unix_client.ml to use CBOR transport
- Add comprehensive directive tests (test/cram/directives.t)
The CBOR transport provides more compact binary encoding compared to
JSON-RPC, which is beneficial for web worker communication.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>