perf(channelserver): cache rengoku_data.bin at startup

Load and validate rengoku_data.bin once during server initialization
instead of reading it from disk on every client request. The file is
static ECD-encrypted config data (~4.9 KB) that never changes at
runtime. Validation checks file size and ECD magic bytes, logging a
warning if the file is missing or invalid so misconfiguration is
caught before any client connects.

server/channelserver/handlers_rengoku.go

@@ -3,8 +3,6 @@ package channelserver
 import (
 	"encoding/binary"
 	ps "erupe-ce/common/pascalstring"
-	"os"
-	"path/filepath"
 
 	"erupe-ce/common/byteframe"
 	"erupe-ce/network/mhfpacket"
@@ -180,10 +178,8 @@ func handleMsgMhfLoadRengokuData(s *Session, p mhfpacket.MHFPacket) {
 
 func handleMsgMhfGetRengokuBinary(s *Session, p mhfpacket.MHFPacket) {
 	pkt := p.(*mhfpacket.MsgMhfGetRengokuBinary)
-	// a (massively out of date) version resides in the game's /dat/ folder or up to date can be pulled from packets
-	data, err := os.ReadFile(filepath.Join(s.server.erupeConfig.BinPath, "rengoku_data.bin"))
-	if err != nil {
-		s.logger.Error("Failed to read rengoku_data.bin", zap.Error(err))
+	data := s.server.rengokuBin
+	if data == nil {
 		doAckBufFail(s, pkt.AckHandle, nil)
 		return
 	}