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.

network/mhfpacket/msg_mhf_enumerate_dist_item.go

@@ -13,7 +13,7 @@ type MsgMhfEnumerateDistItem struct {
 	AckHandle uint32
 	DistType  uint8
 	Unk1      uint8
-	Unk2      uint16
+	MaxCount  uint16
 	Unk3      []byte
 }
 
@@ -27,7 +27,7 @@ func (m *MsgMhfEnumerateDistItem) Parse(bf *byteframe.ByteFrame, ctx *clientctx.
 	m.AckHandle = bf.ReadUint32()
 	m.DistType = bf.ReadUint8()
 	m.Unk1 = bf.ReadUint8()
-	m.Unk2 = bf.ReadUint16() // Maximum? Hardcoded to 256
+	m.MaxCount = bf.ReadUint16() // Hardcoded to 256
 	if _config.ErupeConfig.RealClientMode >= _config.Z1 {
 		m.Unk3 = bf.ReadBytes(uint(bf.ReadUint8()))
 	}