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.