fix(js_top_worker): OxCaml demo support, exec RPC fix, and dependency cleanup
- Add comprehensive JS stubs for OxCaml-specific primitives (domain TLS,
arch detection, blocking sync, basement/capsule) needed by the OxCaml
js_of_ocaml runtime
- Fix demo.js to load rpc_worker.bc.js (JSON-RPC) instead of the
non-RPC _opam/worker.js, fixing a protocol mismatch bug
- Fix exec RPC method never resolving: rename phrase_p parameter from
~name:"string" to unnamed, preventing rpclib from incorrectly treating
the phrase as a named parameter in the dispatch dict
- Remove unused cbort, zarith, bytesrw dependencies from opam and
dune-project
- Bump dune version in x-ocaml opam files to 3.21 for OxCaml support
- Update cram test expected output for current package list
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>