added struct RequestReply

[eldoccc]

allows send() and recv() to be cancel safe : they both take mutable references to the struct

in the case of recv() being used inside a tokio::select! for example

It should probably be specified that this isn't as safe as the RequestSender / RequestReceiver way as you could try to send a multipart before receiving data in the case of the receiver and vice versa.

[cetra3]

I think because this is not as safe maybe we should investigate another way to do this. I don't want to introduce a footgun here if there is a cleaner way to do it.