Add RFC 2136 DNS UPDATE Message Format Support

Implement encoding and decoding for DNS UPDATE messages (Opcode 5) as specified in RFC 2136.

• Handles the distinct message structure associated with Opcode 5.
• Includes parsing/generating the Zone Section (ZOCOUNT), Prerequisite Section (PRCOUNT), Update Section (UPCOUNT), and Additional Data Section (ADCOUNT) based on counts in the header, replacing the standard QD/AN/NS/AR sections for this Opcode.
• Enables magna to work with dynamic update requests/responses.