Given an Iterable of [key, value] entries, applies the distance function to each key, finding the one closest to the input key, also returning its associated value as well as the related distance; returns undefined only when there are no successful match - that is, all the keys have +inf distance.

Performs a full linear scan unless a distance equal to 0 is encountered, in which case the function returns immediately; otherwise, the algorithm selects the smallest non-infinite distance: if multiple keys happen to have such distance, the selection order is not guaranteed.