Could use Clipper2, as that supports it and is available through C++, so it should be possible to add that as an dependency via an SPM wrapper, too.
I gave it a quick try but failed, as I'm not familiar with how to compile C++ in a way that it can be used with SPM and then how to call that from SPM. This or that might help.
Add an equivalent of turf-buffer.
Could use Clipper2, as that supports it and is available through C++, so it should be possible to add that as an dependency via an SPM wrapper, too.
I gave it a quick try but failed, as I'm not familiar with how to compile C++ in a way that it can be used with SPM and then how to call that from SPM. This or that might help.