Send duration on the single channel query response

[gpunto]

Goal

The single channel query (POST /channels/:channel_type/:channel_id/query, and the v2 distinct channel route POST /api/v2/chat/channels/:channel_type/query) returns the stored channel entry as-is, so the response has no top-level duration. The real backend always sends it on this response, and the channel list response already has it.

Android is switching this response to the generated ChannelStateResponse in GetStream/stream-chat-android#6760, where duration is required. Without it every queryChannel fails to parse on the mock.

Implementation

paginate_message_list now returns a copy of the channel entry with duration merged in, on both the paginated and non-paginated paths. The stored entry in $channel_list is untouched, so the channel list and later queries are unaffected. It's response metadata, so it goes on the response rather than into the recorded channels fixture.

Testing

Covered by the E2E tests that open a channel not already loaded from the list (quoted replies to messages outside the loaded page, unread messages, push notifications).

Checked against a local server: both query routes return duration: "7.11ms" with and without messages.limit, and POST /channels still returns its recorded duration with no duration on the channel entries. ruby -c and rubocop are clean.

Please verify the E2E test runs:

• iOS
  • run 36740772056: passed
• Android
  • run 36740776953 (develop): passed
  • run 36740781524 (Migrate the channel state responses to the generated channel state models stream-chat-android#6760): passed. Every test that failed for the missing duration now passes; test_pushNotification_optionalValuesAreEmpty failed once on the notification not appearing and passed on re-run.
• Flutter
  • run 36740786834: passed