constexpr const std::string instablities

Related to #1

Probably relate: https://quuxplusone.github.io/blog/2023/10/13/constexpr-string-round-2/

This throws errors with GCC, but using clang++ with libc++ (-stdlib=libc++) works.

This is tested on Fedora and Arch.

The char limit needs to be removed ideally.