refactor: Update ParsedMessageOrChoice type to use Message

- Changed the type definition of ParsedMessageOrChoice from Choice | dict[str, Any] to Choice | Message for improved clarity and type safety in message handling.

Author: bradhilton

src/art/tinker/client.py

@@ -14,9 +14,9 @@
 from openai.types.chat.chat_completion import Choice
 from openai.types.completion_usage import CompletionUsage
 
-from art.types import MessageOrChoice, MessagesAndChoices, Tools
+from art.types import Message, MessageOrChoice, MessagesAndChoices, Tools
 
-ParsedMessageOrChoice = Choice | dict[str, Any]
+ParsedMessageOrChoice = Choice | Message
 ParsedMessagesAndChoices = list[ParsedMessageOrChoice]