socket_monitor: extract socket monitoring from etcp_connections, add per-instance context

- New files: transport_layer/socket_monitor.c/h — socket state monitoring with per-instance ctx
- etcp_api: expose get_latency/1s_pkt_count measuring, add etcp_hashrnd for tests
- utun_instance: store socket_monitor per instance, add is_socket_ok check
- topo_node: detect IPv4 addresses with port from listening sockets
- topo_group: use node_name for display in routes
- Makefile.am: add socket_monitor.c to build

src/utun_instance.h

@@ -125,6 +125,7 @@ struct UTUN_INSTANCE {
     // Callback chain for new ETCP connections
     struct etcp_inst_cbk_entry* new_conn_cbks;
     struct etcp_status_cbk_entry* conn_status_cbks;  // instance-level: NEW/UP/DOWN/DELETE
+    struct etcp_socket_cbk_entry* socket_cbks;       // instance-level: socket ADDR/STATUS changes
     void* test_user_ptr;             // Generic user pointer (used by tests)
 
     struct memory_pool* data_pool;// для входных-выходных данных пакета
@@ -135,6 +136,7 @@ struct UTUN_INSTANCE {
     struct ETCP_SOCKET* etcp_sockets;// linked-list
     struct TCP_SOCKET*  tcp_sockets; // linked-list [TCP-only]
     struct stcp_server *stcp_server; // TCP server (single for now)
+    void* socket_monitor;            // SOCKET_MONITOR* (opaque, transport_layer/socket_monitor.c)
     
     // Pending one-shot pings (for callback on PONG or timeout)
     struct PING_CONTEXT* pending_pings;