Packaging VDE for Nix

FYI, I've started working on packaging "modern" VDE for NixOS at https://codeberg.org/natkr/vde-nix (so far: vdeplug4 and vdeplug_slirp). Probably won't end up doing too much maintenance in the long run, but maybe it could eventually serve as a starting point if someone else ends up looking for it.