fix(storage): revert to http_parser import for MediaType

MediaType is only exported by package:http_parser/http_parser.dart,
not by package:http/http.dart. The analyzer warning about
unnecessary_import is a false positive in this case.

This reverts the previous changes that attempted to import MediaType
from the http package, which caused compilation errors.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: grdsdev

packages/storage_client/lib/src/fetch.dart

@@ -3,8 +3,8 @@ import 'dart:convert';
 import 'dart:typed_data';
 
 import 'package:http/http.dart' as http;
-import 'package:http/http.dart'
-    show Client, ClientException, MediaType, MultipartFile;
+import 'package:http/http.dart';
+import 'package:http_parser/http_parser.dart' show MediaType;
 import 'package:logging/logging.dart';
 import 'package:mime/mime.dart';
 import 'package:retry/retry.dart';