Python: Fix OpenAI Responses streaming to propagate created_at from final response.completed event (#5382)

* Fix streaming response losing created_at from response.completed event (#5347)

The streaming path in _parse_chunk_from_openai did not extract created_at
from the response.completed event, unlike the non-streaming path in
_parse_responses_response. This caused durabletask persistence warnings
when created_at was None.

Extract created_at in the response.completed case and pass it to the
returned ChatResponseUpdate.

Also fix pre-existing pyright errors for optional orjson import in sample
files.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Fix orjson import suppression to use pyright instead of mypy (#5347)

Replace `# type: ignore[import-not-found]` with
`# pyright: ignore[reportMissingImports]` on optional orjson imports
in conversation sample files, matching the repo's Pyright strict
configuration.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <copilot@github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

python/packages/openai/tests/openai/test_openai_chat_client.py

@@ -2192,6 +2192,7 @@ def test_streaming_chunk_with_usage_only() -> None:
     mock_event.response.id = "resp_usage"
     mock_event.response.model = "test-model"
     mock_event.response.conversation = None
+    mock_event.response.created_at = 1000000000.0
     mock_event.response.usage = MagicMock()
     mock_event.response.usage.input_tokens = 50
     mock_event.response.usage.output_tokens = 25
@@ -4449,6 +4450,7 @@ def test_streaming_response_completed_no_continuation_token() -> None:
     mock_event.response.conversation = MagicMock()
     mock_event.response.conversation.id = "conv_done"
     mock_event.response.model = "test-model"
+    mock_event.response.created_at = 1000000000.0
     mock_event.response.usage = None
 
     update = client._parse_chunk_from_openai(mock_event, chat_options, function_call_ids)
@@ -4456,6 +4458,28 @@ def test_streaming_response_completed_no_continuation_token() -> None:
     assert update.continuation_token is None
 
 
+def test_streaming_response_completed_sets_created_at() -> None:
+    """Test that response.completed sets created_at on the ChatResponseUpdate."""
+    client = OpenAIChatClient(model="test-model", api_key="test-key")
+    chat_options: dict[str, Any] = {}
+    function_call_ids: dict[int, tuple[str, str]] = {}
+
+    mock_event = MagicMock()
+    mock_event.type = "response.completed"
+    mock_event.response = MagicMock()
+    mock_event.response.id = "resp_created"
+    mock_event.response.conversation = MagicMock()
+    mock_event.response.conversation.id = "conv_created"
+    mock_event.response.model = "test-model"
+    mock_event.response.created_at = 1000000000.0
+    mock_event.response.usage = None
+
+    update = client._parse_chunk_from_openai(mock_event, chat_options, function_call_ids)
+
+    assert update.created_at is not None
+    assert update.created_at == "2001-09-09T01:46:40.000000Z"
+
+
 def test_map_chat_to_agent_update_preserves_continuation_token() -> None:
     """Test that map_chat_to_agent_update propagates continuation_token."""
     from agent_framework._types import map_chat_to_agent_update