message: Add comments for spec constants.
diff: @@ -26,10 +26,28 @@ EXTENDS Naturals, FiniteSets, Sequences, TLC, FiniteSetsExt, SequencesExt, Funct
  \* Server states
  CONSTANTS
  + \* See original Raft paper (https://www.usenix.org/system/files/conference/atc14/atc14-paper-ongaro.pdf)
  + \* and comments for leadership_state in../src/consensus/aft/raft.h for details on the Follower,
  + \* Candidate, and Leader states.
  Follower,
  Candidate,
  Leader,
  + \* CCF adds the RetiredLeader state to the protocol: A Leader transitions to RetiredLeader
  + \* after committing a reconfiguration transaction which removes the Leader from the
  + \* configuration (see also ../src/consensus/aft/raft.h).
  + \* More formally:
  + \* /\ [][\E s \in Servers: state'[s] = RetiredLeader => state[s] = Leader]_state
  + \* /\ [][\A s \in Servers:
  + \* /\ state[s] = Leader
  + \* /\ CurrentConfiguration(s) \ CurrentConfiguration(s)' = {s}
  + \* => state'[s] = RetiredLeader]_state
  RetiredLeader,
  + \* The node has passed attestation checks, but is waiting for member confirmation,
  + \* and just isn't part of any configurations at all, nor has a communication channel
  + \* with other nodes (Pending is *not* Learner in
  + \* https://microsoft.github.io/CCF/main/architecture/consensus/1tx-reconfig.html).
  + \* More formally:
  + \* \A i \in Servers : state[i] = Pending => i \notin { GetServerSet(s) : s \in Servers}
  Pending
  States == {
  