fix: mypy chatkit errors

[quettabit]

before:

(openai-chatkit) ➜  chatkit-python git:(main) mypy chatkit
chatkit/actions.py:26: error: "TType" is a type variable and only valid in type context  [misc]
chatkit/server.py:381: error: Incompatible types in assignment (expression has type "ThreadMetadata", variable has type "Thread")  [assignment]
chatkit/server.py:429: error: Incompatible types in assignment (expression has type "ThreadMetadata", variable has type "Thread")  [assignment]
chatkit/server.py:443: error: Incompatible types in assignment (expression has type "ThreadMetadata", variable has type "Thread")  [assignment]
chatkit/server.py:522: error: Name "item" already defined on line 490  [no-redef]
chatkit/server.py:544: error: Argument 3 to "action" of "ChatKitServer" has incompatible type "UserMessageItem | AssistantMessageItem | ClientToolCallItem | WidgetItem | WorkflowItem | TaskItem | HiddenContextItem | EndOfTurnItem"; expected "WidgetItem | None"  [arg-type]
chatkit/agents.py:389: error: Incompatible types in assignment (expression has type "ThreadCreatedEvent | ThreadUpdatedEvent | ThreadItemDoneEvent | ThreadItemAddedEvent | ThreadItemUpdated | ThreadItemRemovedEvent | ThreadItemReplacedEvent | ProgressUpdateEvent | ErrorEvent | NoticeEvent", variable has type "RawResponsesStreamEvent | RunItemStreamEvent | AgentUpdatedStreamEvent | _EventWrapper")  [assignment]
chatkit/agents.py:389: note: Items in the first union not in the second: "ThreadCreatedEvent", "ThreadUpdatedEvent", "ThreadItemDoneEvent", "ThreadItemAddedEvent", "ThreadItemUpdated", "ThreadItemRemovedEvent", "ThreadItemReplacedEvent", "ProgressUpdateEvent", "ErrorEvent", "NoticeEvent"
chatkit/agents.py:391: error: "_EventWrapper" has no attribute "type"  [attr-defined]
chatkit/agents.py:392: error: "_EventWrapper" has no attribute "type"  [attr-defined]
chatkit/agents.py:397: error: "_EventWrapper" has no attribute "item"  [attr-defined]
chatkit/agents.py:398: error: "_EventWrapper" has no attribute "item"  [attr-defined]
chatkit/agents.py:399: error: "_EventWrapper" has no attribute "item"  [attr-defined]
chatkit/agents.py:405: error: "_EventWrapper" has no attribute "type"  [attr-defined]
chatkit/agents.py:406: error: "_EventWrapper" has no attribute "item"  [attr-defined]
chatkit/agents.py:408: error: "_EventWrapper" has no attribute "item"  [attr-defined]
chatkit/agents.py:412: error: "_EventWrapper" has no attribute "item"  [attr-defined]
chatkit/agents.py:413: error: Incompatible types in "yield" (actual type "_EventWrapper", expected type "ThreadCreatedEvent | ThreadUpdatedEvent | ThreadItemDoneEvent | ThreadItemAddedEvent | ThreadItemUpdated | ThreadItemRemovedEvent | ThreadItemReplacedEvent | ProgressUpdateEvent | ErrorEvent | NoticeEvent")  [misc]
chatkit/agents.py:417: error: Incompatible types in assignment (expression has type "MessageOutputItem | HandoffCallItem | HandoffOutputItem | ToolCallItem | ToolCallOutputItem | ReasoningItem | MCPListToolsItem | MCPApprovalRequestItem | MCPApprovalResponseItem", variable has type "RawResponsesStreamEvent | RunItemStreamEvent | AgentUpdatedStreamEvent | _EventWrapper")  [assignment]
chatkit/agents.py:433: error: Incompatible types in assignment (expression has type "ResponseAudioDeltaEvent | ResponseAudioDoneEvent | ResponseAudioTranscriptDeltaEvent | ResponseAudioTranscriptDoneEvent | ResponseCodeInterpreterCallCodeDeltaEvent | <48 more items>", variable has type "RawResponsesStreamEvent | RunItemStreamEvent | AgentUpdatedStreamEvent | _EventWrapper")  [assignment]
chatkit/agents.py:433: note: Items in the first union not in the second: "ResponseAudioDeltaEvent", "ResponseAudioDoneEvent", "ResponseAudioTranscriptDeltaEvent", "ResponseAudioTranscriptDoneEvent", "ResponseCodeInterpreterCallCodeDeltaEvent", "ResponseCodeInterpreterCallCodeDoneEvent", "ResponseCodeInterpreterCallCompletedEvent", "ResponseCodeInterpreterCallInProgressEvent", "ResponseCodeInterpreterCallInterpretingEvent", "ResponseCompletedEvent", "ResponseContentPartAddedEvent", "ResponseContentPartDoneEvent", "ResponseCreatedEvent", "ResponseErrorEvent", "ResponseFileSearchCallCompletedEvent", "ResponseFileSearchCallInProgressEvent", "ResponseFileSearchCallSearchingEvent", "ResponseFunctionCallArgumentsDeltaEvent", "ResponseFunctionCallArgumentsDoneEvent", "ResponseInProgressEvent", "ResponseFailedEvent", "ResponseIncompleteEvent", "ResponseOutputItemAddedEvent", "ResponseOutputItemDoneEvent", "ResponseReasoningSummaryPartAddedEvent", "ResponseReasoningSummaryPartDoneEvent", "ResponseReasoningSummaryTextDeltaEvent", "ResponseReasoningSummaryTextDoneEvent", "ResponseReasoningTextDeltaEvent", "ResponseReasoningTextDoneEvent", "ResponseRefusalDeltaEvent", "ResponseRefusalDoneEvent", "ResponseTextDeltaEvent", "ResponseTextDoneEvent", "ResponseWebSearchCallCompletedEvent", "ResponseWebSearchCallInProgressEvent", "ResponseWebSearchCallSearchingEvent", "ResponseImageGenCallCompletedEvent", "ResponseImageGenCallGeneratingEvent", "ResponseImageGenCallInProgressEvent", "ResponseImageGenCallPartialImageEvent", "ResponseMcpCallArgumentsDeltaEvent", "ResponseMcpCallArgumentsDoneEvent", "ResponseMcpCallCompletedEvent", "ResponseMcpCallFailedEvent", "ResponseMcpCallInProgressEvent", "ResponseMcpListToolsCompletedEvent", "ResponseMcpListToolsFailedEvent", "ResponseMcpListToolsInProgressEvent", "ResponseOutputTextAnnotationAddedEvent", "ResponseQueuedEvent", "ResponseCustomToolCallInputDeltaEvent", "ResponseCustomToolCallInputDoneEvent"
chatkit/agents.py:624: error: Incompatible types in "yield" (actual type "Markdown | Text", expected type "TWidget")  [misc]
chatkit/agents.py:625: error: Incompatible types in "yield" (actual type "Markdown | Text", expected type "TWidget")  [misc]
chatkit/agents.py:722: error: Incompatible return value type (got "list[Message]", expected "EasyInputMessageParam | Message | ResponseOutputMessageParam | ResponseFileSearchToolCallParam | ResponseComputerToolCallParam | <16 more items> | list[EasyInputMessageParam | Message | ResponseOutputMessageParam | ResponseFileSearchToolCallParam | ResponseComputerToolCallParam | <16 more items>] | None")  [return-value]
Found 22 errors in 3 files (checked 10 source files)

after:

(openai-chatkit) ➜  chatkit-python git:(qb/mypy) mypy chatkit
Success: no issues found in 10 source files