I've never tried `unordered_flat_map` and would probably prefer to keep Boost, Poco, Qt, and other mega-frameworks outside of this repo to make the builds leane

I've never tried `unordered_flat_map` and would probably prefer to keep Boost, Poco, Qt, and other mega-frameworks outside of this repo to make the builds leaner, but I'm open to alternatives. Which are the best to look into?