feature: support serialize and deserialize class with private member fields

[ding-hai]

hi @ukabuer
This pr is used to support support serialize and deserialize the class with private member fields.
All we need to do is just providing setter and getter function for those private member fields.
such as

class User {
private:
  Gender gender = Gender::Male;
public:
  int age = 1;
  double height = 180.0;
  double value = 1.0;
  
  Gender get_gender() const {return gender;}
  bool set_gender(const Gender& new_gender)  {
    gender = new_gender; 
    return gender == Gender::Male;
  }
  double get_value() const {return value;}
  void set_value(double new_value)  { value = new_value;}
  
  double get_height() const {return height;}
  void set_height(double new_value)  { height = new_value;}
};

namespace seria {
template <> auto register_object<User>() {
  return std::make_tuple(member("age", &User::age, 32),
                         member("gender", &User::set_gender,  &User::get_gender, Gender::Female),
                         member("value", &User::set_value, &User::get_value),
                         member("height", &User::set_height, &User::get_height, 175.5));
}
}

you can get more info from the unit test.