terminal: Add MOVED label support using last_moved_timestamp.

[Aquastar2304]

What does this PR do, and why?

This PR adds support for displaying a “MOVED” label on messages whose
last_moved_timestamp field is present, consistent with the new server API behavior introduced after feature level 365.

Previously, Zulip Terminal only detected edited messages using the last_edit_timestamp or by scanning edit_history.
With the server now sending last_moved_timestamp, clients no longer need to infer message movement from history.

This PR brings the terminal client in line with web-app behavior by:

 1.Adding a new label MOVED when last_moved_timestamp is set.
 2.Ensuring EDITED takes priority when both timestamps exist.
 3.Updating MessageBox logic to match the new server contract.
 4.Adding automated tests to validate the label behavior.

This helps Zulip Terminal remain API-compatible and visually consistent with other Zulip clients.

Outstanding aspect(s)

• [ ]

External discussion & connections

• Discussed in #zulip-terminal in topic
• Fully fixes #
• Partially fixes issue #
• Builds upon previous unmerged work in PR #
• Is a follow-up to work in PR #
• Requires merge of PR #
• Merge will enable work on #

How did you test this?

• Manually - Behavioral changes
• Manually - Visual changes
• [ x ] Adapting existing automated tests
• [ x ] Adding automated tests for new behavior (or missing tests)
• Existing automated tests should already cover this (only a refactor of tested code)

Self-review checklist for each commit

• [ x ] It is a minimal coherent idea
• [ x ] It has a commit summary following the documented style (title & body)
• [ x ] It has a commit summary describing the motivation and reasoning for the change
• [ x ] It individually passes linting and tests
• [ x ] It contains test additions for any new behavior
• [ x ] It flows clearly from a previous branch commit, and/or prepares for the next commit

Visual changes