[LLC, Persistence] Add doc comments

Signed-off-by: Sahil Kumar <[email protected]>

packages/dart_client/lib/src/models/message.dart

@@ -72,7 +72,7 @@ class Message {
   @JsonKey(includeIfNull: false, toJson: Serialization.readOnly)
   final List<Reaction> ownReactions;
 
-  /// The ID of the parent message, if the message is a reply.
+  /// The ID of the parent message, if the message is a thread reply.
   final String parentId;
 
   /// A quoted reply message

packages/dart_client/lib/src/models/reaction.dart

@@ -29,7 +29,7 @@ class Reaction {
   @JsonKey(includeIfNull: false, toJson: Serialization.readOnly)
   final String userId;
 
-  /// The score of the reaction (ie. number of reactions sent)
+  /// Reaction custom extraData
   @JsonKey(includeIfNull: false)
   final Map<String, dynamic> extraData;