rlmesh_env_server_new
New binds. start runs callbacks on library threads; serve keeps lane 0 on the caller. shutdown is allowed from a callback. Free shuts down and drains all C callbacks, including any still running past the facade's timeout.
RLMeshStatus rlmesh_env_server_new(
RLMeshEnv* const* envs,
size_t envs_len,
const RLMeshEnvServerOptions* options,
RLMeshEnvServer** out
)