feat(master): login stamps travel through master and back

The login's Stamps now go with auth's REQUEST_ZONE_TRANSFER to master and
come back in REQUEST_ZONE_TRANSFER_RESPONSE, so master stamps the steps it
performs itself, with its own time: got the request
(WORLD_PACKET_RECEIVED, zone), the world is still starting and the request
waits (IM_LOGIN_QUEUED, instance), answered with a world
(WORLD_SESSION_CONFIRM_TO_AUTH, instance). Auth sends what comes back in
the login response.

Server to server wire change (message IDs unchanged): both messages end
with a Stamps list (u32 16 * count + 4, then the stamps); it is empty
(4 bytes) when a world server asks for a transfer. Touched:
- MasterPackets::SendZoneTransferRequest / SendZoneTransferResponse: take
  and write the stamps (default empty)
- MasterServer.cpp REQUEST_ZONE_TRANSFER: reads them, stamps, keeps them
  in the PendingInstanceRequest (new stamps member, InstanceManager.h)
- InstanceManager::ReadyInstance / AffirmTransfer: stamp and send them back
- ZoneInstanceManager: HandleRequestZoneTransferResponse reads them; a
  RequestZoneTransfer overload takes stamps and a callback that gets them
- AuthPackets LoginRequest::Handle uses that overload

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

dMasterServer/InstanceManager.h

@@ -6,6 +6,7 @@
 #include "dCommonVars.h"
 #include "IServerOperations.h"
 #include "RakNetTypes.h"
+#include "Stamps.h"
 #include "dZMCommon.h"
 #include "Logger.h"
 
@@ -18,6 +19,7 @@ struct PendingInstanceRequest {
 	uint64_t id;
 	bool mythranShift;
 	SystemAddress sysAddr;
+	Stamps stamps; // The login stamps that came with the request; they go back in the response
 };
 
 class Instance {