Both operands are size_t (unsigned), so if readPos > data.size() the
subtraction wrapped to ~0 instead of returning 0. This could happen
via setReadPos() which has no bounds check. Downstream hasRemaining()
was already safe but getRemainingSize() callers (e.g. hasFullPackedGuid)
would see billions of bytes available.
Add writePackedGuid() to Packet class for read/write symmetry. Remove
now-redundant UpdateObjectParser::readPackedGuid and
MovementPacket::writePackedGuid static methods. Replace 6 internal
readPackedGuid calls, 9 writePackedGuid calls, and 1 inline 14-line
transport GUID write with Packet method calls.
Move packed GUID reading into Packet class alongside readUInt8/readFloat.
Replace 121 UpdateObjectParser::readPackedGuid(packet) calls with
packet.readPackedGuid() across 4 files, reducing coupling between
Packet and UpdateObjectParser.
Add Packet::hasFullPackedGuid() method and remove identical standalone
definitions from game_handler.cpp and packet_parsers_classic.cpp.
Replace 53 free-function calls with method calls.
Add getRemainingSize() one-liner to Packet class and replace all 656
instances of getSize()-getReadPos() across game_handler, world_packets,
and both packet parser files.
