Covers byTsOldToNew, byOrderKey (undefined-last + the no-equality-branch
quirk for two present keys), and the factory comparators
factoryRoomIdByUnreadCount / factoryRoomIdByActivity / factoryRoomIdByAtoZ
(activity-desc, unread-desc, A–Z case-insensitive with leading-# stripped)
using minimal MatrixClient mocks. Full suite now 108 tests.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
