code: func WithPeerSorter(value PeerSorter) copts.Opt {
  	return func(p copts.Params) {
  		if setter, ok := p.(peerSorterSetter); ok {
  			setter.SetPeerSorter(value)
  		}
  	}
  }
docs: // WithPeerSorter sets a peer sorter function which provides per-request
  // sorting of peers