Potential for Runtime Json Improvements

[TheNitesWhoSay]

Currently I solve the problem of reading types known at runtime time with "Json::Generic"s - relying on polymorphism - but I could potentially (though not necessarily, will need performance testing before and after) cut a lot of memory usage and processing overhead using a type index (or type hash or whatnot) and some sort of union'd type.

In this example I'm using tuple, which is of course not union'd and thus not addressing memory usage, but it demonstrates dynamically retrieving the type from a pack of template parameters. https://godbolt.org/z/z1o818

Generics are also currently ~800 lines of code with tons of repetition for the pure virtual methods, getting this metric down would also be nice if possible.