Ensure CoinNet behaves correctly in each adversarial scenario

[hewison-chris]

• [ ] Model the maximum delay that an attacker can create with and without incurring financial penalty;
• [ ] Model under which condition a node or a cabal could censor honest nodes;
• [ ] Test which error paths are the most expensive (with and without authentication);
• [ ] Model more adversarial scenarios with the team and add them to agora.test;