C++26 reflection adoption

[lixin-wei]

@liuzicheng1987 It might be too early to discuss now. but I'm curious whether you're willing to use C++26's reflection to repalce the core part of this library? like num_fields.hpp, bind_to_tuple.hpp. We can use a macro to detect C++ version and switch automatically.

If you are happy about this idea I'm willing to volunteer in the future once there is a stable compiler :)

[liuzicheng1987]

@lixin-wei Absolutely, that's the plan.