Extend ApplyEntry in JetStreamMetaGroup with PeerAdd/PeerRemove dispatch
to the existing Task 12 peer management methods. Add StreamMsgOp (Store,
Remove, Purge) and ConsumerOp (Ack, Nak, Deliver, Term, Progress) enums
plus ApplyStreamMsgOp and ApplyConsumerEntry methods to StreamReplicaGroup.
Extend ApplyCommittedEntriesAsync to parse smsg:/centry: command prefixes
and route to the new apply methods. Add MetaEntryType.PeerAdd/PeerRemove
enum values. 35 new tests in EntryApplicationTests.cs, all passing.
