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>

tests/dGameTests/dGameMessagesTests/SkillMessagesTests.cpp

@@ -30,7 +30,7 @@ namespace {
 	template<typename Legacy>
 	PacketBytes LegacyPacket(LWOOBJID target, Legacy& legacy) {
 		RakNet::BitStream bitStream;
-		BitStreamUtils::WriteHeader(bitStream, ServiceType::CLIENT, MessageType::Client::GAME_MSG);
+		LUBitStream(ServiceType::CLIENT, MessageType::Client::GAME_MSG).WriteHeader(bitStream);
 		bitStream.Write(target);
 		legacy.Serialize(bitStream);
 		return FromBitStream(bitStream);
@@ -262,7 +262,7 @@ TEST_F(SkillMessagesTests, EchoesBroadcastExceptTheCaster) {
 	const auto caster = ClientAddress();
 	const auto legacy = Capture([&] {
 		RakNet::BitStream bitStreamLocal;
-		BitStreamUtils::WriteHeader(bitStreamLocal, ServiceType::CLIENT, MessageType::Client::GAME_MSG);
+		LUBitStream(ServiceType::CLIENT, MessageType::Client::GAME_MSG).WriteHeader(bitStreamLocal);
 		bitStreamLocal.Write(echo.target);
 		LegacyGameMessages::EchoSyncSkill legacyEcho("ab", 0, 0, true);
 		legacyEcho.Serialize(bitStreamLocal);