Python: Thread storage and serialization (#394)

* Updates for message store support

* Added unit tests

* Added suspend-resume example

* Added example with custom chat message store

* Small fix

* Addressed PR feedback

* Renaming and documentation

* More renaming

* Addressed more PR feedback

* Small fixes in Foundry chat client and examples

* Small update

* Addressed PR feedback

* Increased timeout for Azure tests

python/samples/getting_started/agents/openai_chat_client/openai_chat_client_with_thread.py

@@ -4,7 +4,7 @@ import asyncio
 from random import randint
 from typing import Annotated
 
-from agent_framework import ChatClientAgent, ChatClientAgentThread
+from agent_framework import AgentThread, ChatClientAgent, ChatMessageList
 from agent_framework.openai import OpenAIChatClient
 from pydantic import Field
 
@@ -87,7 +87,6 @@ async def example_with_existing_thread_messages() -> None:
 
     # Start a conversation and build up message history
     thread = agent.get_new_thread()
-    assert isinstance(thread, ChatClientAgentThread)  # Ensure we have the right type
 
     query1 = "What's the weather in Paris?"
     print(f"User: {query1}")
@@ -95,7 +94,9 @@ async def example_with_existing_thread_messages() -> None:
     print(f"Agent: {result1.text}")
 
     # The thread now contains the conversation history in memory
-    message_count = len(thread.chat_messages or [])
+    messages = await thread.list_messages()
+
+    message_count = len(messages or [])
     print(f"Thread contains {message_count} messages")
 
     print("\n--- Continuing with the same thread in a new agent instance ---")
@@ -117,8 +118,9 @@ async def example_with_existing_thread_messages() -> None:
     print("\n--- Alternative: Creating a new thread from existing messages ---")
 
     # You can also create a new thread from existing messages
-    existing_messages = thread.chat_messages or []
-    new_thread = ChatClientAgentThread(messages=existing_messages)
+    messages = await thread.list_messages()
+
+    new_thread = AgentThread(message_store=ChatMessageList(messages))
 
     query3 = "How does the Paris weather compare to London?"
     print(f"User: {query3}")