Update to async-openai 0.16.2

[Dreaming-Codes]

Following the recent API update of ChatGPT, Async OpenAI has undergone numerous modifications in its codebase, necessitating significant adjustments to align this library with the updated version.

[zurawiki]

What specific features are needed in the newer version of this OpenAI crate?

I only want to upgrade if necessary because changing dependency versions can break consumers of this tiktoken-rs crate.

[Dreaming-Codes]

What specific features are needed in the newer version of this OpenAI crate?

I only want to upgrade if necessary because changing dependency versions can break consumers of this tiktoken-rs crate.

The latest version adds support for chatgpt threads, chatgpt vision and calling multiple functions at once

[Dreaming-Codes]

It might be better to submit a pull request to async-openai, integrating this library into that lib, rather than the other way around. This is because they are more prone to changes from OpenAI than this library is.