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

dotnet-examples/speech-enhancement-gtcrn/Program.cs

@@ -0,0 +1,45 @@
+// Copyright (c)  2025  Xiaomi Corporation
+//
+// This file shows how to use speech enhancement API with GTCRN models.
+//
+// 1. Download a model from
+// https://github.com/k2-fsa/sherpa-onnx/releases/tag/speech-enhancement-models
+//
+// wget https://github.com/k2-fsa/sherpa-onnx/releases/download/speech-enhancement-models/gtcrn_simple.onnx
+//
+// 2. Download a test file
+//
+// wget https://github.com/k2-fsa/sherpa-onnx/releases/download/speech-enhancement-models/inp_16k.wav
+//
+// 3. Now run it
+//
+// dotnet run
+
+using SherpaOnnx;
+
+class OfflineSpeechEnhancementDemo
+{
+  static void Main(string[] args)
+  {
+    var config = new OfflineSpeechDenoiserConfig();
+    config.Model.Gtcrn.Model = "./gtcrn_simple.onnx";
+    config.Model.Debug = 1;
+    config.Model.NumThreads = 1;
+    var sd = new OfflineSpeechDenoiser(config);
+
+    WaveReader waveReader = new WaveReader("./inp_16k.wav");
+    var denoisedAudio =  sd.Run(waveReader.Samples, waveReader.SampleRate);
+
+    var outputFilename = "./enhanced-16k.wav";
+    var ok = denoisedAudio.SaveToWaveFile(outputFilename);
+
+    if (ok)
+    {
+      Console.WriteLine($"Wrote to {outputFilename} succeeded!");
+    }
+    else
+    {
+      Console.WriteLine($"Failed to write {outputFilename}");
+    }
+  }
+}