Feat/responses api

[nezhyborets]

What

Ability to work with models through Responses API.

OpenAI's most advanced interface for generating model responses. Supports text and image inputs, and text outputs. Create stateful interactions with the model, using the output of previous responses as input. Extend the model's capabilities with built-in tools for file search, web search, computer use, and more. Allow the model access to external systems and data using function calling.

Why

There have already been requests for it: https://github.com/MacPaw/OpenAI/issues/298. And it seems that OpenAI is making it the default way to interact with models:

If you're a new user, we recommend using the Responses API. (https://platform.openai.com/docs/guides/responses-vs-chat-completions)

Affected Areas

Non of the existing public API have changed, but the deployment target is introduced with iOS 13 (macOS 10.15) minimum. Internally - refactoring of OpenAI class by extracting "internal clients" so that they can be reused in other "public clients" like newly introduced ResponsesEndpoint.