Keep hidden channels out of the channel list when member or channel updates arrive - #6697

Goal

A channel hidden via channel.hidden is put back into the channel list by a channel.updated or
member.updated for the same channel, and stays there until the app restarts. The remove itself works: in the
reported logs the displayed grouped list empties and then has the channel back 38ms later, inside the same event
batch. Neither add path checks whether the channel is hidden.

Closes AND-1530

Implementation

• Skip the add in DefaultChatEventHandler.addIfMembershipUpdated when the cached channel is hidden. This is the
  member.updated path, and it is the only one that applies to plain channel lists, since the base handler
  already skips channel.updated.
• Skip it in GroupAwareChatEventHandler.routeByGroup when the cached channel is hidden, and remove the channel if
  it is still listed. This is the channel.updated path; the default group resolver always resolves a channel into
  the all sentinel group, so an all grouped query took the add unconditionally.

hidden is per-user and absent from channel.updated payloads, so both guards read the cached channel. Per-channel
event handling runs before query handling in the same batch, so for a channel whose state is active in memory the
flag is current. parseChatEventResults falls back to the database for channels that are not active, and the
database is only written after query handling, so on that fallback the guard sees the pre-batch value and does not
fire. Narrowing that gap means filtering hidden where the query map is written rather than per event, which is a
wider change than this fix.

The new-message add paths stay unguarded: a non-shadowed message clears hidden in ChannelEventHandler, which is
what makes a hidden channel resurface legitimately.

ChannelMutableState.toChannel() now resolves the current user from the userFlow it already holds instead of the
ChatClient singleton. Same value (StateRegistry is constructed with clientState.user), and it lets the state
layer be exercised without a built client.

Testing

• New EventHandlerSequentialHiddenChannelTest drives EventHandlerSequential over the real StateRegistry and
  LogicRegistry. It replays the reported batch (notification.mark_read, channel.hidden, channel.updated,
  member.updated) against a grouped query, and covers a plain query hidden in one batch and updated in the next.
  Both fail without the guards. A third case asserts the same batch without the hidden event still adds the channel,
  so the assertions cannot pass vacuously, and a fourth asserts a new message brings a hidden channel back.
• Unit coverage for each guard in DefaultChatEventHandlerTest and GroupAwareChatEventHandlerTest, including a
  hidden channel already in the list being removed.
• Verified on a device with the Compose sample, driving the backend through the Stream CLI. Built from this branch's
  base and from the branch itself, so the builds differ only by the fix. On the base build a channel hidden with
  HideChannel is put back into the list by the following UpdateMemberPartial; on the fix build it stays out, and
  a new message still brings it back. The backend excludes the channel from that user's QueryChannels response
  throughout, so a list that shows it is provably out of sync with the server.
• The channel.updated path is grouped-only, and grouped queries are restricted server-side to a single org, so it
  is covered by the automated tests here and validated by the reporter rather than in a sample app.

Summary by CodeRabbit

• Bug Fixes
  • Hidden channels are no longer re-added to standard or grouped channel queries by membership or channel updates.
  • Hidden channels can return to queries when a new message or visibility update makes them visible.
  • Membership updates now correctly respect channel visibility and the currently connected user.
  • Unread counts now report zero when no user is connected and remain scoped to the active user.
• Tests
  • Added coverage for hidden-channel event ordering, membership updates, grouped queries, and unread counts.