Single round-trip optimization for Paxos with PaxosLease masters

In the previous article, I combined Paxos and PaxosLease into a small master-based replicated state machine. The obvious inefficiency was that every command still ran a full two-phase Paxos round. In this article, I add the simplest possible optimization: once a node has become master and completed one full Paxos round, later fresh log slots can skip the prepare phase and go directly to propose.