D4: Add hash segment support to ReplyMapper (_GR_.{cluster}.{hash}.{reply}), FNV-1a ComputeReplyHash, TryExtractClusterId/Hash, legacy format compat. D5: Add ConnectSolicitedAsync with exponential backoff (1s-60s cap), JetStreamDomain propagation in LEAF handshake, LeafNodeOptions.JetStreamDomain.