refactor(byteframe): replace read-overflow panic with sticky error

ByteFrame previously panicked on out-of-bounds reads, which crashed
the server when parsing malformed client packets. Now sets a sticky
error (checked via Err()) and returns zero values, matching the
encoding/binary scanner pattern. The session recv loop checks Err()
after parsing to reject malformed packets gracefully.

Also replaces remaining panic("Not implemented") stubs in network
packet Build/Parse methods with proper error returns.

network/binpacket/msg_bin_mail_notify.go

@@ -1,6 +1,8 @@
 package binpacket
 
 import (
+	"fmt"
+
 	"erupe-ce/common/byteframe"
 	"erupe-ce/common/stringsupport"
 	"erupe-ce/network"
@@ -13,7 +15,7 @@ type MsgBinMailNotify struct {
 
 // Parse parses the packet from binary.
 func (m MsgBinMailNotify) Parse(bf *byteframe.ByteFrame) error {
-	panic("implement me")
+	return fmt.Errorf("MsgBinMailNotify.Parse: not implemented")
 }
 
 // Build builds a binary packet from the current data.