refactor(dart): refactor dart structure

refactor dart structure

Author: simeng-li

lib/interfaces/logto_interfaces.dart

@@ -1,4 +1,4 @@
-import '/interfaces/logto_config.dart';
+import '/src/interfaces/logto_config.dart';
 
 // Logto SDK
 class Logto {

lib/interfaces/oidc_provider_config.dart

@@ -1,5 +1,4 @@
-import 'interfaces/logto_interfaces.dart';
-import 'utilities/utils.dart';
+import '/src/utilities/utils.dart';
 
 class Core {
   static const String codeChallengeMethod = 'S256';

lib/logto_client.dart

@@ -0,0 +1 @@
+export 'logto_config.dart';

lib/logto_core.dart

@@ -1,14 +1,15 @@
 import 'package:flutter_test/flutter_test.dart';
 
-import 'package:logto_dart_sdk/interfaces/logto_config.dart';
+import 'package:logto_dart_sdk/src/interfaces/logto_config.dart';
 import 'package:logto_dart_sdk/logto_client.dart';
 
 void main() {
   test(' Init Logto Instance', () {
     const String appId = 'foo';
     const String endpoint = 'foo@siverhand.io';
 
-    final config = LogtoConfig(appId: 'foo', endpoint: 'foo@siverhand.io');
+    const config = LogtoConfig(appId: 'foo', endpoint: 'foo@siverhand.io');
+
     final logto = Logto(config);
 
     expect(logto.config.appId, appId);