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.

src/proxy/tcp_proxy_server.c

@@ -107,10 +107,14 @@ 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;
-    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);
+    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) {

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;