Show HN: Cjson.cpp, the new fastest-ever (constexpr) JSON parser

Howdy.

This is a fully constexpr (mostly, the mapping + vector marshalling code isn't) JSON parsing library for C++23/26. Based off of my preliminary benchmarks it's around 30-80% faster in parsing json (of any form) compared to the fastest libraries I could find (simdjson/Glaze). In serialization & DOM manipulation (which is mostly what I've written this for), it's outright 3-10x faster (depending on the doc). The only weak(ish) spot is the fact that it parses number heavy jsons slightly worse (it's double parser isn't too heavily optimized) plus it suffers (a bit) on super tiny inputs (sub 100ish bytes).

The other important feature is the fact that the _whole_ library is constexpr, allowing you to do full json parsing + mutations at compiletime, which is especially useful for build system dispatching via #embed.