Use allocators

[chocolacula]

Most of operations in reflection code should be type agnostic. This is the reason why classes like Box or Sequence don't have a type parameter. We really don't know what the type is within Box and this is the reason why we have some problem with allocators.

see https://github.com/chocolacula/easy_reflection_cpp/blob/3d917138bba34fed4524626c9dd611e75f243b5a/library/include/er/reflection/actions.h#L13

Perhaps we can write some adaptor for allocators and use something like std::allocator<uint8_t> and cast pointers for objects.