Expose registrator accessor for runtime REGISTER customization

Author: mechtech-mind

lib/src/sip_ua_helper.dart

@@ -3,6 +3,7 @@ import 'dart:async';
 import 'package:flutter_webrtc/flutter_webrtc.dart';
 import 'package:logger/logger.dart';
 import 'package:sdp_transform/sdp_transform.dart' as sdp_transform;
+import 'package:sip_ua/src/registrator.dart';
 
 import 'package:sip_ua/src/uri.dart';
 import 'config.dart';
@@ -35,6 +36,7 @@ class SIPUAHelper extends EventManager {
   }
 
   UA? _ua;
+  Registrator? get registrator => _ua?.registratorInstance;
   Settings _settings = Settings();
   UaSettings? _uaSettings;
   final Map<String?, Call> _calls = <String?, Call>{};

lib/src/ua.dart

@@ -78,6 +78,7 @@ class Contact {
  * @throws {TypeError} If no configuration is given.
  */
 class UA extends EventManager {
+  Registrator get registratorInstance => _registrator;
   UA(Settings configuration) {
     logger.d('new() [configuration:${configuration.toString()}]');
     // Load configuration.