generateSerialNumber abstract method
Generates a unique serial number (SN) for message content.
The SN serves as a unique message ID (uint64) to track and deduplicate messages.
msgType is the type of the message content (used for algorithm-specific generation).
now is the timestamp to incorporate into the SN (or current time if null).
Returns a 64-bit unsigned integer (uint64) as the unique serial number.
Implementation
int generateSerialNumber(String? msgType, DateTime? now);