tqwewe/kameo

AI Summary: The task is to debug and fix a panic in the Kameo Rust library that occurs when calling `stop_gracefully()` on an already stopped actor. The issue stems from a type conversion error within the error handling, specifically when converting a `tokio::sync::mpsc::error::SendError` to a `kameo::error::SendError`. The solution involves modifying the error handling to gracefully handle the case where the actor is already stopped, likely by returning a specific error type indicating this condition instead of panicking.