add buildin relay support, fix remote signer some bugs

lib/util/ip_util.dart

@@ -0,0 +1,19 @@
+import 'dart:io';
+
+class IpUtil {
+  static Future<String?> getIp() async {
+    var ips = await NetworkInterface.list();
+    for (var interface in ips) {
+      print('== Interface: ${interface.name} ==');
+      if (interface.name == "WLAN") {
+        for (var addr in interface.addresses) {
+          print(
+              '${addr.address} ${addr.host} ${addr.isLoopback} ${addr.rawAddress} ${addr.type.name}');
+          return addr.address;
+        }
+      }
+    }
+
+    return ips.first.addresses.first.address;
+  }
+}