refactor: enhance chat message handling and scrolling behavior

- Added `sendMessageWithContainer` function to facilitate message sending with a ProviderContainer.
- Updated `_ChatPageState` to improve scroll behavior, ensuring smoother auto-scrolling when near the bottom of the chat.
- Refactored scroll logic to simplify conditions for showing and hiding the scroll-to-bottom button.
- Adjusted the `OptimizedList` widget to correctly handle item indexing based on the reverse property, enhancing list performance and usability.

lib/features/chat/providers/chat_providers.dart

@@ -1447,6 +1447,15 @@ Future<void> sendMessageFromService(
   await _sendMessageInternal(ref, message, attachments, toolIds);
 }
 
+Future<void> sendMessageWithContainer(
+  ProviderContainer container,
+  String message,
+  List<String>? attachments, [
+  List<String>? toolIds,
+]) async {
+  await _sendMessageInternal(container, message, attachments, toolIds);
+}
+
 // Internal send message implementation
 Future<void> _sendMessageInternal(
   dynamic ref,