refactor: move CDN files to cdn directory

Moves CDN-related files from the `file` directory to a new `cdn` directory.

Author: xsahil03x

…s/stream_feeds/lib/src/file/cdn_api.dart …es/stream_feeds/lib/src/cdn/cdn_api.dartpackages/stream_feeds/lib/src/file/cdn_api.dart renamed to packages/stream_feeds/lib/src/cdn/cdn_api.dart packages/stream_feeds/lib/src/file/cdn_api.dart renamed to packages/stream_feeds/lib/src/cdn/cdn_api.dart

@@ -2,9 +2,9 @@ import 'dart:async';
 
 import 'package:stream_core/stream_core.dart';
 
+import '../cdn/cdn_api.dart';
+import '../cdn/feeds_cdn_client.dart';
 import '../feeds_client.dart';
-import '../file/cdn_api.dart';
-import '../file/feeds_cdn_client.dart';
 import '../generated/api/api.dart' as api;
 import '../models/activity_data.dart';
 import '../models/app_data.dart';