awaitLeader

Suspend until a voter in the mesh holds RaftRole.Leader; return it.

Races all voters' RaftNode.role StateFlows: the first voter to emit RaftRole.Leader wins and is returned. Under virtual time (test dispatcher) the test scheduler drives this; in tests prefer us.tractat.kuilt.raft.test.MultiNodeRaftSim.awaitLeader for bounded await with election-thrash detection.