uploadAvatar method
override
Uploads a new profile photo to NTUT Portal, replacing the current one.
oldFilename should be the current avatar filename
(from UserDto.avatarFilename, or empty string if none).
Returns the new avatar filename assigned by the server.
Implementation
@override
Future<String> uploadAvatar(Uint8List imageBytes, String? oldFilename) async {
return uploadAvatarResult ?? '111590001_temp1052748000000.jpeg';
}