fix(client): handle keepalive events in streaming responses

[othelot]

Recently, OpenAI started returning keepalive events in Streaming Event, which is an issue reported by other projects.

Resolve the following errors.

failed to deserialize api response: error:unknown variant `keepalive`, expected one of `response.created`, `response.in_progress`, `response.completed`, `response.failed`, `response.incomplete`, `response.output_item.added`, `response.output_item.done`, `response.content_part.added`, `response.content_part.done`, `response.output_text.delta`, `response.output_text.done`, `response.refusal.delta`, `response.refusal.done`, `response.function_call_arguments.delta`, `response.function_call_arguments.done`, `response.file_search_call.in_progress`, `response.file_search_call.searching`, `response.file_search_call.completed`, `response.web_search_call.in_progress`, `response.web_search_call.searching`, `response.web_search_call.completed`, `response.reasoning_summary_part.added`, `response.reasoning_summary_part.done`, `response.reasoning_summary_text.delta`, `response.reasoning_summary_text.done`, `response.reasoning_text.delta`, `response.reasoning_text.done`, `response.image_generation_call.completed`, `response.image_generation_call.generating`, `response.image_generation_call.in_progress`, `response.image_generation_call.partial_image`, `response.mcp_call_arguments.delta`, `response.mcp_call_arguments.done`, `response.mcp_call.completed`, `response.mcp_call.failed`, `response.mcp_call.in_progress`, `response.mcp_list_tools.completed`, `response.mcp_list_tools.failed`, `response.mcp_list_tools.in_progress`, `response.code_interpreter_call.in_progress`, `response.code_interpreter_call.interpreting`, `response.code_interpreter_call.completed`, `response.code_interpreter_call_code.delta`, `response.code_interpreter_call_code.done`, `response.output_text.annotation.added`, `response.queued`, `response.custom_tool_call_input.delta`, `response.custom_tool_call_input.done`, `error` at line 1 column 19 content:{"type":"keepalive","sequence_number":3}