Python: OpenAI ResponsesClient omits additional_properties on model call

[jomalsan]

This applies for the Azure OpenAI Responses client as well.

chat_options.additional_properties is not included when building the options dictionary: openai/_responses_client.py:_prepare_options

This matters because it blocks me from passing the additional properties that I need to control a reasoning model. Specifically, I want to set:

additional_properties = {
       "reasoning": { # Controls the reasoning behavior and asks for summaries 
            "effort": "medium",
            "summary": "auto",
        },
        "include": ["reasoning.encrypted_content"], # When store is False, reasoning traces are returned (encrypted) to be resent on follow ups
        "store": False # Set to false for no data retention

[eavanvalkenburg]

Fixed in #1255