Freshest first delivery for the Leios mini-protocols

[coot]

Leios requires the Frishest First Delivery. We're recognising that this might require server-side message reordering. This is not currently possible in typed-protocols framework, where the client and server are agreeing on the state machine. We want to explore a possible design of a request-response like mini-protocol, where there are multiple request types (as in the mini-protocols proposed in the Leios CIP) that could be served in an order that is decided by the server side, which still provides the guarantees of the typed-protocols of deadlock and live-lock freedom.