refactor: remove part of directive

Author: cybex-dev

lib/models/active_call.dart

@@ -1,5 +1,3 @@
-part of twilio_voice;
-
 enum CallDirection { incoming, outgoing }
 
 class ActiveCall {

lib/models/call_event.dart

@@ -1,5 +1,3 @@
-part of twilio_voice;
-
 enum CallEvent {
   incoming,
   ringing,

lib/twilio_voice.dart

@@ -5,8 +5,8 @@ import 'package:twilio_voice/_internal/method_channel/twilio_call_method_channel
 import '_internal/method_channel/twilio_voice_method_channel.dart';
 import '_internal/platform_interface/twilio_voice_platform_interface.dart';
 
-part 'models/active_call.dart';
-part 'models/call_event.dart';
+export './models/active_call.dart';
+export './models/call_event.dart';
 
 class TwilioVoice extends MethodChannelTwilioVoice {
   static TwilioVoicePlatform get instance => MethodChannelTwilioVoice.instance;