Python: [BREAKING] added SerializationMixin and applied to contents, agents, chat client… (#1012)

* added SerializationMixin and applied to contents, agents, chat clients, removed AFBaseModel

* fix annotations type

* mypy fixes

* fix tests

* fix serializable subvalues and added large docstring

* updated indents in code block

* fixed exported urls

python/tests/samples/getting_started/test_threads_samples.py

@@ -0,0 +1,53 @@
+# Copyright (c) Microsoft. All rights reserved.
+
+import copy
+import os
+from collections.abc import Awaitable, Callable
+from typing import Any
+
+import pytest
+from pytest import MonkeyPatch, mark, param
+
+from samples.getting_started.threads.custom_chat_message_store_thread import main as threads_custom_store
+from samples.getting_started.threads.suspend_resume_thread import main as threads_suspend_resume
+
+# Environment variable for controlling sample tests
+RUN_SAMPLES_TESTS = "RUN_SAMPLES_TESTS"
+
+# All thread samples
+thread_samples = [
+    param(
+        threads_custom_store,
+        [],  # Non-interactive sample
+        id="threads_custom_store",
+        marks=[
+            pytest.mark.openai,
+            pytest.mark.skipif(os.getenv(RUN_SAMPLES_TESTS, None) is None, reason="Not running sample tests."),
+        ],
+    ),
+    param(
+        threads_suspend_resume,
+        [],  # Non-interactive sample
+        id="threads_suspend_resume",
+        marks=[
+            pytest.mark.openai,
+            pytest.mark.skipif(os.getenv(RUN_SAMPLES_TESTS, None) is None, reason="Not running sample tests."),
+        ],
+    ),
+]
+
+
+@mark.parametrize("sample, responses", thread_samples)
+async def test_thread_samples(sample: Callable[..., Awaitable[Any]], responses: list[str], monkeypatch: MonkeyPatch):
+    """Test thread samples with input mocking and retry logic."""
+    saved_responses = copy.deepcopy(responses)
+
+    def reset():
+        responses.clear()
+        responses.extend(saved_responses)
+
+    def mock_input(prompt: str = "") -> str:
+        return responses.pop(0) if responses else "exit"
+
+    monkeypatch.setattr("builtins.input", mock_input)
+    await sample