let Message inherit AsAny

[tinglou]

introduce crate as as_any, and let Message inherits AsAny, then dyn Message can downcast to a concrete type easier.
Here is a example,

    fn encode(&self, msg: &dyn Message, buf: &mut Vec<u8>) -> Result<(), TcpTransportError> {
        let msg = msg
            .downcast_ref::<T>()
            .ok_or(TcpTransportError::Infallible)?;

        // println!("type name: {}", msg.type_name());
        msg.encode(buf)?;
        Ok(())
    }

[caspermeijn]

I don't see in what situation this would be an improvement. This is already possible with &dyn Any. Can you explain when this would be useful?