Changes to Create Batch

added the new optional request property requests/items/messages/items/anyOf[subschema #1: MessageCreate]/content/anyOf[subschema #1]/items/oneOf[subschema #1: TextContent]/signature

added the new optional request property requests/items/messages/items/anyOf[subschema #1: MessageCreate]/content/anyOf[subschema #1]/items/oneOf[subschema #3: ToolCallContent]/signature

added the new optional request property requests/items/messages/items/anyOf[subschema #1: MessageCreate]/content/anyOf[subschema #1]/items/oneOf[subschema #7: OmittedReasoningContent]/signature

added the optional property agent_id to the response with the 200 status

added the optional property background to the response with the 200 status