Improve feedback build errors in `css-syntax-patches-for-csstree`

PS: I tried to work on this a little, but got stuck on warnings in the form of _Unmerged patch for property/type …_ which are a bit hard to decipher to be honest. :sweat_smile:

_Originally posted by @tyrasd in https://github.com/csstools/postcss-plugins/issues/1687#issuecomment-3482268682_
            