The project is great. The HN comments are embarrassing. Isn’t it ironic to imply laziness by chiming in with “vibe coded” which in itself is such a lazy reaction.
It is common for header-only libraries: you need to include this header in one c++ using the macro for linking (don't use that macro in other c++ files to avoid duplicate symbols). In C++, you can declare a function as many times as you want, but you can only define it (write the actual body) once in the entire project.