feat: handle multiple tool calls

[vacekj]

fixes #179

feedback wanted!

[0xMochan]

Hey, thanks for this PR. I have a feeling this will greatly break with my upcoming #199 messages refactor. I'll keep an eye our on how this affects this PR and maybe can help rebase / merge from main to assist in the new messages layout.

[vacekj]

@0xMochan sure, I will rebase periodically to ease the merge once you merge yours.

[0xMochan]

@0xMochan sure, I will rebase periodically to ease the merge once you merge yours.

Hey #199 was finally merged, please let me know if you need help rebasing or merging, it was quite an intense commit! Part of multi-tool-calling was resolved but not entirely.

[carlos-verdes]

@vacekj check #290 I think you will like it

[carlos-verdes]

I think this is not correct approach, from the model of OpenAI you can have just one message or 1 to many tool calls:

So I propose something like this:

#[derive(Debug)]
pub enum ModelChoice {
    /// Represents a completion response as a message
    Message(String),
    /// Represents a completion response as a tool call of the form
    /// `ToolCall(function_name, id, function_params)`.
    ToolCalls(OneOrMany<ToolCall>),
}

pub struct ToolCall {
    function_name: String, 
    id: String, 
    function_params: serde_json::Value)
}