feat: Tool.call should accept mutable &self

[klntsky]

• I have looked for existing issues (including closed) about this

Feature Request

Motivation

I want to persist some state in the tool.

Proposal

Change:

    /// The tool execution method.
    /// Both the arguments and return value are a String since these values are meant to
    /// be the output and input of LLM models (respectively)
    fn call(
        &self,
        args: Self::Args,
    ) -> impl Future<Output = Result<Self::Output, Self::Error>> + Send + Sync;

to

    /// The tool execution method.
    /// Both the arguments and return value are a String since these values are meant to
    /// be the output and input of LLM models (respectively)
    fn call(
        &mut self,
        args: Self::Args,
    ) -> impl Future<Output = Result<Self::Output, Self::Error>> + Send + Sync;

Alternatives

Currently, I'm forced to store data behind an Arc, so that I can update it and access later:

#[derive(Deserialize, Serialize)]
pub struct MyTool {
    #[serde(skip)]
    pub state: Arc<Mutex<MyToolRuntime>>,
    #[serde(skip)]
    pub response: Arc<Mutex<Option<MyToolResponse>>>,
}

I'm not sure if there is an easier way right now