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

scripts/dotnet/OfflineSpeechDenoiser.cs

@@ -0,0 +1,64 @@
+/// Copyright (c)  2025  Xiaomi Corporation (authors: Fangjun Kuang)
+
+using System.Runtime.InteropServices;
+
+namespace SherpaOnnx
+{
+    public class OfflineSpeechDenoiser: IDisposable
+    {
+        public OfflineSpeechDenoiser(OfflineSpeechDenoiserConfig config)
+        {
+            IntPtr h = SherpaOnnxCreateOfflineSpeechDenoiser(ref config);
+            _handle = new HandleRef(this, h);
+        }
+
+        public DenoisedAudio Run(float[] samples, int sampleRate)
+        {
+            IntPtr p = SherpaOnnxOfflineSpeechDenoiserRun(_handle.Handle, samples, samples.Length, sampleRate);
+            return new DenoisedAudio(p);
+        }
+
+        public void Dispose()
+        {
+            Cleanup();
+            // Prevent the object from being placed on the
+            // finalization queue
+            System.GC.SuppressFinalize(this);
+        }
+
+        ~OfflineSpeechDenoiser()
+        {
+            Cleanup();
+        }
+
+        private void Cleanup()
+        {
+            SherpaOnnxDestroyOfflineSpeechDenoiser(_handle.Handle);
+
+            // Don't permit the handle to be used again.
+            _handle = new HandleRef(this, IntPtr.Zero);
+        }
+
+        private HandleRef _handle;
+
+        public int SampleRate
+        {
+            get
+            {
+                return SherpaOnnxOfflineSpeechDenoiserGetSampleRate(_handle.Handle);
+            }
+        }
+
+        [DllImport(Dll.Filename)]
+        private static extern IntPtr SherpaOnnxCreateOfflineSpeechDenoiser(ref OfflineSpeechDenoiserConfig config);
+
+        [DllImport(Dll.Filename)]
+        private static extern void SherpaOnnxDestroyOfflineSpeechDenoiser(IntPtr handle);
+
+        [DllImport(Dll.Filename)]
+        private static extern int SherpaOnnxOfflineSpeechDenoiserGetSampleRate(IntPtr handle);
+
+        [DllImport(Dll.Filename)]
+        private static extern IntPtr SherpaOnnxOfflineSpeechDenoiserRun(IntPtr handle, float[] samples, int n, int sampleRate);
+    }
+}