OpenAI responses streaming

[katzdave]

This PR implements support for OpenAI's Responses API with streaming

• Implemented full support for OpenAI's Responses API format with streaming capabilities
• Added new openai_responses.rs format handler for the responses endpoint
• Updated OpenAI provider to handle both chat completions and responses formats
• Improved token counting and usage tracking for the new format

[katzdave]

Still figuring out how to get usage data for the streaming, but otherwise this is working pretty well. Interestingly usage comes through when there's a tool call.

[katzdave]

@michaelneale This seems to be working pretty well for me. Want to take it for test drive?

[cbruyndoncx]

@michaelneale Hi guys , I am doing a project where i need deep research, what is the outlook for this landing in the next release ?