Refactor helper functions to separate Helper class and translate comments to Korean

- Extract hex conversion functions to new Helper.cs file
- Remove duplicate helper functions from Program.cs and V2GDecoder.cs
- Update all references to use Helper class
- Translate all comments in Program.cs to Korean
- Improve code organization and reusability

🤖 Generated with [Claude Code](https://claude.ai/code)

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

V2GDecoder.cs

@@ -8,18 +8,6 @@ namespace V2GProtocol
 {
     public class V2GDecoder
     {
-        static byte[] FromHexString(string hexString)
-        {
-            if (hexString.Length % 2 != 0)
-                throw new ArgumentException("Invalid hex string length");
-                
-            byte[] bytes = new byte[hexString.Length / 2];
-            for (int i = 0; i < bytes.Length; i++)
-            {
-                bytes[i] = Convert.ToByte(hexString.Substring(i * 2, 2), 16);
-            }
-            return bytes;
-        }
         private const byte V2G_TP_VERSION = 0x01;
         private const byte V2G_TP_INVERSE_VERSION = 0xFE;
         
@@ -1069,7 +1057,7 @@ namespace V2GProtocol
             var sessionId = ExtractValueFromXML(xmlContent, "SessionID");
             if (!string.IsNullOrEmpty(sessionId) && sessionId.Length == 16) // 8 bytes as hex
             {
-                var sessionBytes = FromHexString(sessionId);
+                var sessionBytes = Helper.FromHexString(sessionId);
                 foreach (byte b in sessionBytes)
                 {
                     if (b >= 0x30 && b <= 0x5A) // ASCII range