Derive Macro Agent 

#[derive(Agent)]
{
    // Attributes available to this derive:
    #[agent]
}

Derives agents::agent::Agent by delegating to an inner field marked with #[agent].

use agents::{Agent, SessionAgent};

#[derive(Agent)]
struct EchoAgent {
    #[agent]
    inner: SessionAgent<String, (), (), String>,
}