Split online.cs and offline.csFile (#941)

Co-authored-by: 东风破 <birdfishs@163.com>

scripts/dotnet/OfflineTdnnModelConfig.cs

@@ -0,0 +1,22 @@
+/// Copyright (c)  2024.5 by 东风破
+
+using System.Linq;
+using System.Collections.Generic;
+using System.Runtime.InteropServices;
+using System.Text;
+using System;
+
+namespace SherpaOnnx
+{
+    [StructLayout(LayoutKind.Sequential)]
+    public struct OfflineTdnnModelConfig
+    {
+        public OfflineTdnnModelConfig()
+        {
+            Model = "";
+        }
+        [MarshalAs(UnmanagedType.LPStr)]
+        public string Model;
+    }
+
+}