Keep metadata when starts and ends are sorted in the same way (i.e. out of order intervals)

[sjvenditto]

Right now whenever starts and ends are sorted, metadata is always dropped since the constructor doesn't know how whether to align the metadata to the sorted start or sorted end times. We should make an exception and keep metadata when they are sorted in the same way, in the case when intervals are just out of order and not actually changed, which has a clear mapping back to the metadata.

A simple fix to this is just to use argsort in place of sort and compare that the indices match between start and end sorts in order to keep metadata