Dynamic Modules Added Cluster Worker Fan Out And Worker Slot

Added ABI primitives for publishing main-thread state out to worker threads on the cluster dynamic-module extension: envoy_dynamic_module_callback_cluster_run_on_all_workers (with the matching envoy_dynamic_module_on_cluster_worker_event hook) fans an event out to every registered worker; envoy_dynamic_module_callback_cluster_worker_slot_set / envoy_dynamic_module_callback_cluster_worker_slot_get (with the matching envoy_dynamic_module_on_cluster_worker_slot_data_destroy cleanup hook) publish an opaque payload into a worker thread-local slot and read it back. The Rust SDK adds matching Cluster::on_worker_event, EnvoyCluster::run_on_all_workers, and an EnvoyClusterWorkerSlotExt extension trait with type-safe worker_slot_set<T>(Arc<T>) / worker_slot_get<T>() -> Option<Arc<T>>.