read_decided_suffix unnecessary LogEntry wrapper

[kevin-harrison]

Right now when a user calls Omnipaxos::read_decided_suffix() they receive a LogEntry struct which wraps an entry in order to show if the entry is decided or not. Seeing as it will always be decided this is unnecessary. We can simply return an Entry instead.

[kevin-harrison]

On second thought this isn't possible, because read_decided_suffix() needs to return more than just an Entry type since it can return StopSign and Compacted types. Therefore, we need a enum such as LogEntry to wrap the possible return types. It is still awkward here for users to have to pattern match on LogEntry::Undecided(Entry). We could return a DecidedLogEntry enum which removes this awkwardness at the cost of most more complexity.