chore: fix lints

Author: xsahil03x

packages/stream_chat_flutter/lib/src/ai_assistant/ai_typing_indicator_view.dart

@@ -118,6 +118,7 @@ class AnimatedDots extends StatelessWidget {
         ...List.generate(
           count,
           (index) => _AnimatedDot(
+            key: ValueKey(index),
             index: index,
             size: size,
             color: color,

packages/stream_chat_flutter/lib/src/ai_assistant/stream_typewriter_builder.dart

@@ -1,6 +1,5 @@
 import 'dart:async';
 import 'dart:math';
-import 'package:characters/characters.dart';
 
 import 'package:flutter/widgets.dart';