Add C# API for speech enhancement GTCRN models (#1990)

scripts/dotnet/OfflineSpeechDenoiserConfig.cs

@@ -0,0 +1,16 @@
+/// Copyright (c)  2025  Xiaomi Corporation (authors: Fangjun Kuang)
+
+using System.Runtime.InteropServices;
+
+namespace SherpaOnnx
+{
+    [StructLayout(LayoutKind.Sequential)]
+    public struct OfflineSpeechDenoiserConfig
+    {
+        public OfflineSpeechDenoiserConfig()
+        {
+            Model = new OfflineSpeechDenoiserModelConfig();
+        }
+        public OfflineSpeechDenoiserModelConfig Model;
+    }
+}