refactor: add Packet::readPackedGuid() and replace 121 static 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.

include/network/packet.hpp

@@ -27,6 +27,7 @@ public:
     uint32_t readUInt32();
     uint64_t readUInt64();
     float readFloat();
+    uint64_t readPackedGuid();
     std::string readString();
 
     uint16_t getOpcode() const { return opcode; }