tcp_proxy: fix throughput (tx_queue backpressure) + connect timeout + integration test

- Router: unified service delivery format [svc_id][src][dst][payload] (end-to-end src/dst from SVC_ROUTE header)
- tcp_proxy_client: replace single tx_buf drop-on-backpressure with bounded tx_queue + send_q waiter + retry timer (no data loss, bulk window reopen — removes 62.5ms delayed-ACK stall)
- tcp_io: configurable connect timeout (tcp_conn_set_connect_timeout)
- tcp_proxy_server: connect_timeout config option (ms, default 2000, 0=off)
- check.sh: run tcp_proxy_full integration test with sudo (skip if passwordless sudo unavailable)
- test_tcp_io: connect timeout unit test; docs (lwip_nuances.md)

src/config_parser.h

@@ -196,6 +196,7 @@ struct global_config {
     int      tcp_proxy_server_so_mark;      // Linux SO_MARK, 0=не менять
     uint32_t tcp_proxy_server_netif_index;  // Linux SO_BINDTODEVICE, 0=нет
     char     tcp_proxy_server_bind_ip[64];  // IP для bind() перед connect()
+    int      tcp_proxy_server_connect_timeout_ms;  // таймаут connect(), мс (0 = без таймаута)
 
     // NTP configuration ([ntp] section)
     int ntp_enabled;