Add support for reasoning context in Responses

[joseharriaga]

ResponseReasoningOptions should have a property called Context of type ResponseReasoningContext?. ResponseReasoningContext is a new extensible enum that must be added with the values "Auto", "CurrentTurn", and "AllTurns".

For more info, see: https://developers.openai.com/api/reference/resources/responses/methods/create#(resource)%20responses%20%3E%20(method)%20create%20%3E%20(params)%200.non_streaming%20%3E%20(param)%20reasoning%20%3E%20(schema)%20%2B%20(resource)%20%24shared%20%3E%20(model)%20reasoning%20%3E%20(schema)%20%3E%20(property)%20context

To validate, test that the returned ResponseResult include the same Context value in its ReasoningOptions property.