fix: use-after-free in pkt_normalizer + ll_queue waiter cancel + uasync gen counter for epoll fd-reuse

- pkt_normalizer: save recvpart->len before queue_data_put (may free synchronously)
- ll_queue: save uasync_call_soon handle in queue_waiter_handle, cancel on free
- uasync: generation counter in epoll data.u64 to skip stale events after fd reuse
- uasync: keep fd_to_index mapping after socket_array_remove for inactive nodes
- test: test_uasync_socket_race — 4 children × 200 iterations, currently flaky

lib/ll_queue.h

@@ -117,6 +117,7 @@ struct queue_waiter_handle {
     struct ll_queue*     defer_q;
     queue_threshold_callback_fn defer_cb;
     void*                defer_arg;
+    void*                call_soon_id;       ///< хендл отложенного вызова (для отмены)
 };
 
 /**