VersionedIntervalTimeline uses different comparators for the same version type

In most places, `String` is used as the version type for `VersionedIntervalTimeline`. However, the users of this class use two different comparators in different places. For example, in `AppenderatorImpl`, `String.CASE_INSENSITIVE_ORDER` is used as the comparator while `Comparator.naturalOrder()` is used as the comparator in `VersionedIntervalTimeline.forSegments()`. I think perhaps this might not be very critical but it would be better to use the same comparator.

Start by inspecting VersionedIntervalTimeline.forSegments() and the comparator passed by AppenderatorImpl, then search for other VersionedIntervalTimeline call sites using String versions. Determine which ordering is intended and verify the consistent comparator behavior with the relevant existing tests or a focused regression test.

Written by the indexing model from the issue text.