Add concurrency documentation to MetadataSegmentView

`MetadataSegmentView` lacks [concurrency documentation](https://github.com/code-review-checklists/java-concurrency#documentation).

FYI @surekhasaharan

Locate the MetadataSegmentView class and inspect its existing documentation and concurrency-related behavior. Add the missing concurrency documentation referenced by the issue, and verify that the class documentation clearly describes its concurrency expectations.

Written by the indexing model from the issue text.