refactor: remove the packet macros, WriteHeader and PacketUtils

Nothing in the server writes or reads a packet by hand any more, so the
helpers for doing so go:
- CBITSTREAM, CMSGHEADER, CINSTREAM, CINSTREAM_SKIP_HEADER, SEND_PACKET,
  SEND_PACKET_BROADCAST and HEADER_SIZE leave dCommonVars.h;
- the free BitStreamUtils::WriteHeader (LUBitStream::WriteHeader writes the
  same bytes) and the unused PacketUtils::SavePacket are deleted.
The last raw reads are replaced: WorldServer builds its input stream
directly, the master packet logs read the header with
LUBitStream::ReadHeader instead of peeking at packet->data[1] and [3], and
MessageInspector reads a sent game message's header with the new
NetGameMsg::ReadPacketHeader (the counterpart of WritePacket) instead of
memcmp/memcpy. packet->data[0] is still compared with RakNet's own
connection IDs.

The frozen oracles keep using the macros verbatim through the test-only
tests/dGameTests/LegacyPacketMacros.h; the HeaderSkip tests, which only
tested CINSTREAM_SKIP_HEADER, are removed.

docs/PacketArchitecture.md: "where we are" now describes the final state
and what still touches raw bytes (RakNet IDs, replica headers, behavior bit
streams), and a new section collects the known wire discrepancies found
during the conversion, with client addresses.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

dNet/BitStreamUtils.cpp

@@ -1,7 +1,6 @@
 #include "BitStreamUtils.h"
 #include "dServer.h"
 #include "BitStream.h"
-#include "PacketUtils.h"
 
 
 void LUBitStream::WriteHeader(RakNet::BitStream& bitStream) const {

dNet/BitStreamUtils.h

@@ -75,16 +75,7 @@ struct LUBitStream {
 };
 
 
-#define BITSTREAMUTILS_HAS_WRITEHEADER
 namespace BitStreamUtils {
-	template<typename T>
-	void WriteHeader(RakNet::BitStream& bitStream, ServiceType connectionType, T internalPacketID) {
-		bitStream.Write<MessageID>(ID_USER_PACKET_ENUM);
-		bitStream.Write<ServiceType>(connectionType);
-		bitStream.Write(static_cast<uint32_t>(internalPacketID));
-		bitStream.Write<uint8_t>(0);
-	}
-
 	/**
 	 * Writes an optional ("default flag") field: one bit saying whether value differs from defaultValue, then
 	 * the value itself only if it does. This is how the client encodes game message parameters that have a default.

dNet/CMakeLists.txt

@@ -6,7 +6,6 @@ set(DNET_SOURCES "AuthPackets.cpp"
 	"dServer.cpp"
 	"MailInfo.cpp"
 	"MasterPackets.cpp"
-	"PacketUtils.cpp"
 	"Stamps.cpp"
 	"WorldPackets.cpp"
 	"WorldRoutePacket.cpp"