Fix concurrency of VersionedIntervalTimeline

`getAllTimelineEntries()` allows accessing a collection that might be modified concurrently. See https://github.com/code-review-checklists/java-concurrency#unsafe-concurrent-iteration

Start by locating getAllTimelineEntries() and its callers, then read the surrounding VersionedIntervalTimeline implementation and the linked unsafe-iteration guidance. Trace how the returned collection is used under concurrent modification; done means the method no longer exposes unsafe concurrent iteration and relevant regression coverage passes.

Written by the indexing model from the issue text.