7404ecdb0e
- Add cached state properties (LastSeq, MessageCount, TotalBytes, FirstSeq) to IStreamStore/FileStore/MemStore — eliminates GetStateAsync on publish path - Add Capture(StreamHandle, ...) overload to StreamManager — eliminates double FindBySubject lookup (once in JetStreamPublisher, once in Capture) - Remove _messageIndexes dictionary from FileStore write path — all lookups now use _messages directly, saving ~48B allocation per message - Add JetStreamPubAckFormatter for hand-rolled UTF-8 success ack formatting — avoids JsonSerializer overhead on the hot publish path - Switch flush loop to exponential backoff (1→2→4→8ms) matching Go server