fix: concurrent modification and last message update

The `channels.keys` iterable is now cloned before iteration to prevent concurrent modification exceptions.

Additionally, the logic for updating a channel's `lastMessageAt` timestamp has been corrected to consider all messages, not just the very last one.

Author: xsahil03x

packages/stream_chat/lib/src/client/channel.dart

@@ -3530,8 +3530,11 @@ class ChannelClientState {
 
     // Calculate the new last message at time.
     var lastMessageAt = _channelState.channel?.lastMessageAt;
-    final lastMessage = updatedChannelMessages.lastOrNull;
-    if (lastMessage != null && _shouldUpdateChannelLastMessageAt(lastMessage)) {
+    final lastMessage = updatedChannelMessages.lastWhereOrNull(
+      _shouldUpdateChannelLastMessageAt,
+    );
+
+    if (lastMessage != null) {
       lastMessageAt = [lastMessageAt, lastMessage.createdAt].nonNulls.max;
     }
 

packages/stream_chat/lib/src/client/client.dart

@@ -2291,7 +2291,7 @@ class ClientState {
 
         // Iterate through all the available channels and send the event
         // to be handled by the respective channel instances.
-        for (final cid in channels.keys) {
+        for (final cid in [...channels.keys]) {
           final channelEvent = event.copyWith(cid: cid);
           _client.handleEvent(channelEvent);
         }