feat: message pruning

[isekovanic]

🎯 Goal

Wires up the message list window cap from GetStream/stream-chat-js#1875, so a livestream channel stops growing its loaded window forever.

🛠 Implementation details

The cap now lives in LLC config, so <Channel maximumMessageLimit> is removed.

// before
<Channel maximumMessageLimit={100} />

// after
channel.messagePaginator.updateConfig({ maxLoadedItems: 100 });
// or declaratively, per surface
client.config.set({ channel: { messagePaginator: { maxLoadedItems: 100 } } });

Everything that read the prop now reads the config through useStateStore(paginator.configState, …), so the three maximumMessageLimit scroll branches in MessageList / MessageFlashList keep working unchanged.

usePrunableMessageList keeps its viewability tracking and the isNearEnd heuristic, but instead of pruning itself it pushes one boolean into the paginator — setPruningSuspended(isNearEnd(...)) - and the LLC prunes on ingest. It lifts the suspension on unmount, otherwise a list that goes away would pin the window open forever.

Also fixes a real bug while it's in here: MessageFlashList never reset its pagination trackers after a prune. #3254 fixed that in MessageList only.

Needs the LLC PR merged and an rc published before CI can pass - the stream-chat pin has to move with it.

🎨 UI Changes

🧪 Testing

☑️ Checklist

• I have signed the Stream CLA (required)
• PR targets the develop branch
• Documentation is updated
• New code is tested in main example apps, including all possible scenarios
  • SampleApp iOS and Android
  • Expo iOS and Android