refactor(mhfpacket): rename 15 Unk fields with identified meanings

Replace unknown field names with descriptive names based on handler
logic analysis, switch dispatch patterns, DB query context, and
inline comments:

- ObjectHandleID, IsQuest, ItemIDCount, MaxCount, TokenLength,
  FormatVersion, LogoutType (high confidence from comments/constants)
- QueryType, DataType, MissionIndex, CheckOnly, RequestType,
  ExchangeType, TournamentID (confirmed by handler switch/if usage)

Also fix MsgSysLogout.Build calling ReadUint8 instead of WriteUint8.

server/channelserver/handlers_tournament_test.go

@@ -12,7 +12,7 @@ func TestHandleMsgMhfInfoTournament_Type0(t *testing.T) {
 
 	pkt := &mhfpacket.MsgMhfInfoTournament{
 		AckHandle: 12345,
-		Unk0:      0,
+		QueryType:      0,
 	}
 
 	handleMsgMhfInfoTournament(session, pkt)
@@ -34,7 +34,7 @@ func TestHandleMsgMhfInfoTournament_Type1(t *testing.T) {
 
 	pkt := &mhfpacket.MsgMhfInfoTournament{
 		AckHandle: 12345,
-		Unk0:      1,
+		QueryType:      1,
 	}
 
 	handleMsgMhfInfoTournament(session, pkt)