Add support for LZ11-compressed BCH files

LZ11BCH.cs

@@ -0,0 +1,54 @@
+using System;
+using System.IO;
+using Toolbox.Core;
+
+namespace CtrLibrary
+{
+    /// <summary>
+    /// Handles BCH files wrapped in Nintendo LZ11 compression while retaining
+    /// the original .bch extension.
+    /// </summary>
+    public class LZ11BCH : ICompressionFormat
+    {
+        public string[] Description { get; } = new[] { "Nintendo LZ11 BCH Compression" };
+
+        public string[] Extension { get; } = new[] { "*.bch" };
+
+        public bool CanCompress => true;
+
+        public bool Identify(Stream stream, string fileName)
+        {
+            if (!fileName.EndsWith(".bch", StringComparison.OrdinalIgnoreCase))
+                return false;
+
+            byte[] data = stream.ToArray();
+            if (data.Length < 5 || data[0] != 0x11)
+                return false;
+
+            try
+            {
+                using (var decompressed = new LZSS_N().Decompress(new MemoryStream(data, false)))
+                {
+                    return decompressed.Length >= 3 &&
+                           decompressed.ReadByte() == 'B' &&
+                           decompressed.ReadByte() == 'C' &&
+                           decompressed.ReadByte() == 'H';
+                }
+            }
+            catch
+            {
+                return false;
+            }
+        }
+
+        public Stream Decompress(Stream stream)
+        {
+            return new LZSS_N().Decompress(stream);
+        }
+
+        public Stream Compress(Stream stream)
+        {
+            return new LZSS_N().Compress(stream);
+        }
+    }
+}