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).
msgType is the message type identifier (for type-specific SN generation).
now is the timestamp (defaults to current time if null).
Returns a unique serial number (uint64) for the message.
Implementation
int generateSerialNumber(String? msgType, DateTime? now);