chore: more upgrades for channel_header_theme.dart

* Renamed:
  * title -> titleStyle
  * subtitle -> subtitleStyle
* Added
  * ==
  * hashcode
  * debugFillProperties
  * lerp

packages/stream_chat_flutter/lib/src/channel_info.dart

@@ -64,7 +64,7 @@ class ChannelInfo extends StatelessWidget {
         style: StreamChatTheme.of(context)
             .channelTheme
             .channelHeaderTheme
-            .subtitle,
+            .subtitleStyle,
       );
     } else {
       final userId = StreamChat.of(context).currentUser?.id;