Add migrated to .NET 8.0 variant of Hcs.Client

Hcs.ClientNet/GostXades/Helpers/ConvertHelper.cs

@@ -0,0 +1,12 @@
+using System.Numerics;
+
+namespace GostXades.Helpers
+{
+    public static class ConvertHelper
+    {
+        public static string BigIntegerToHex(string str)
+        {
+            return BigInteger.Parse(str).ToString("X");
+        }
+    }
+}