EasyPacket<T>.fromJson constructor
根据Map创建新实例
Implementation
factory EasyPacket.fromJson(Map<String, dynamic> map) {
return EasyPacket._(
route: map['route'],
id: map['id'],
code: map['code'],
desc: map['desc'],
data: map['data'],
ucid: map['ucid'],
word: map['word'],
sign: map['sign'],
);
}