Handle Out-of-Order Messages

[tyurek]

The current test program for protocol.rs simulates the random message ordering of distributed protocols by arbitrarily choosing a player to act at each step. However, this is not sufficient to model arbitrary message ordering as if message A causes message B, B will appear later in the message queue.

To fix the test, change

let message: Message = deserialize!(&self.inbox.remove(0))?;

to

let index = rng.gen_range(0..self.inbox.len());
let message: Message = deserialize!(&self.inbox.remove(index))?;

in process_single_message()

This change reveals some bugs in the protocol implementation (both on the main branch and in PR #32). Namely, an out-of-order message will cause a player to attempt to retrieve data from storage that has not yet been put into storage, causing a runtime BailError("Could not find StorableIndex {[omitted]} when getting from storage"). Most of the time, the program will crash attempting to retrieve a missing RoundOnePrivate, but occasionally the execution gets far enough to crash on a missing RoundOnePublic. Fixing these may likely reveal additional issues.