generateSerialNumber abstract method
Generates a unique serial number (SN) for message identification.
Creates a cryptographically unique or time-based serial number to uniquely identify a message (used for tracking, deduplication, and receipts).
@param msgType - Optional message type identifier (for type-specific SN generation)
@param now - Optional timestamp (defaults to current time if null)
@return Unique serial number for the message
Implementation
int generateSerialNumber(String? msgType, DateTime? now);