fix: use-after-free in tcp_conn_destroy + throttle consumer_ack

tcp_conn_destroy: set read/write queue callbacks to NULL before
queue_free to stop deferred autofetch (drain_cb on freed rc).

write_on_get_cb: throttle consumer_ack to every 8th write_queue
dequeue instead of every single one (was 30+ ACK/sec).

ack_batch field in tcp_proxy_server_conn.

lib/tcp_io.c

@@ -105,6 +105,8 @@ void tcp_conn_destroy(struct tcp_conn* tc) {
     }
     queue_waiter_cancel(tc->read_queue, &tc->read_waiter);
     queue_set_empty_callback(tc->read_queue, NULL, NULL);
+    queue_set_callback(tc->read_queue, NULL, NULL);
+    queue_set_callback(tc->write_queue, NULL, NULL);
 
     struct ll_entry* e;
     while ((e = queue_data_get(tc->read_queue)) != NULL) {

src/proxy/tcp_proxy_server.c

@@ -107,11 +107,15 @@ static void write_on_get_cb(struct ll_queue* q, void* arg) {
     struct tcp_proxy_server_conn* rc = (struct tcp_proxy_server_conn*)arg;
     struct UTUN_INSTANCE* inst = rc->ctx ? rc->ctx->inst : NULL;
     if (!inst) return;
+    rc->ack_batch++;
+    if (rc->ack_batch >= 8) {
+        rc->ack_batch = 0;
         DEBUG_DEBUG(DEBUG_CATEGORY_SOCKET, "SOCK:ACK fd=%d sid=%08x write_q=%d",
                     rc->tc ? (int)rc->tc->sock : -1, rc->stream_id,
                     queue_entry_count(q));
         etcp_router_consumer_ack(inst, rc->peer_node_id, ETCP_ID_TCP_PROXY);
     }
+}
 
 static void on_fin_cb(struct tcp_conn* tc, void* arg) {
     struct tcp_proxy_server_conn* rc = (struct tcp_proxy_server_conn*)arg;

src/proxy/tcp_proxy_server.h

@@ -36,6 +36,7 @@ struct tcp_proxy_server_conn {
     void*    close_timer;      // таймер повтора CLOSE/ERROR
     int      close_backoff;    // backoff: 50..5000 tb (5ms..500ms)
     void*    diag_timer;       // 1-секундный таймер диагностики
+    uint8_t  ack_batch;        // счётчик для throttled consumer_ack (каждые 8 записей)
 
     struct queue_waiter_handle pause_waiter;
     struct UASYNC* ua;