Add support for the OpenAI API

[levigross]

This PR enables basic support for OpenAI models (and endpoints that expose a OpenAI API compatible API interface).

I am stressing on basic support because we will leave tool calling to the next PR :)

[gemini-code-assist[bot]]

Summary of Changes

Hello @levigross, I'm Gemini Code Assist[^1]! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request lays the groundwork for integrating OpenAI models into the system. It establishes the necessary components to send requests, process responses, and manage streaming interactions with OpenAI's API, ensuring compatibility with existing LLM interfaces. The current implementation focuses on core generation capabilities, with plans to extend support for advanced features like tool calling in future iterations.

Highlights

• OpenAI API Integration: Introduced basic support for interacting with the OpenAI API, enabling the system to send requests to OpenAI models and compatible endpoints.
• Dependency Management: Added the official github.com/openai/openai-go/v3 Go client library and several github.com/tidwall JSON utility libraries to go.mod and go.sum.
• Core OpenAI Model Implementation: Created a new openai package under model/ with openAIModel implementing the model.LLM interface, handling both streaming and non-streaming content generation.
• Request and Response Conversion: Developed comprehensive logic to convert generic LLMRequest objects into OpenAI-specific request parameters and to transform OpenAI API responses back into the generic genai.GenerateContentResponse format.
• Streaming Event Handling: Implemented a streamTranslator to process and buffer OpenAI streaming events, particularly for accumulating function call arguments, ensuring proper reconstruction of streamed responses.
• Error Handling and Constants: Defined specific error types (errors.go) and event type constants (consts.go) for the OpenAI integration to improve clarity and maintainability.

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[levigross]

@gemini-code-assist please rereview this code

[levigross]

@dpasiukevich What do I need to do to get this PR reviewed? 😀

[YouChenJun]

Thank you for contributing this PR to add support for the OpenAI API! This is a highly valuable feature that will greatly improve the flexibility of the project. We noticed there are some merge conflicts now. Could you please help resolve them when you have time? This will help move the PR forward for merging. Let us know if you need any support from our side. Thanks again for your great work! @levigross

[YouChenJun]

Thank you for contributing this PR to add support for the OpenAI API! This is a highly valuable feature that will greatly improve the flexibility of the project. We noticed there are some merge conflicts now. Could you please help resolve them when you have time? This will help move the PR forward for merging. Let us know if you need any support from our side. Thanks again for your great work! @levigross