Added asynchronous version of the Hash method (#122)

Co-authored-by: boris <[email protected]>

Author: rubanbs

src/ImageHash/ImageHashExtensions.cs

@@ -2,6 +2,8 @@ namespace CoenM.ImageHash
 {
     using System;
     using System.IO;
+    using System.Threading;
+    using System.Threading.Tasks;
     using SixLabors.ImageSharp;
     using SixLabors.ImageSharp.PixelFormats;
 
@@ -31,5 +33,28 @@ public static ulong Hash(this IImageHash hashImplementation, Stream stream)
             using var image = Image.Load<Rgba32>(stream);
             return hashImplementation.Hash(image);
         }
+
+        /// <summary>Asynchronously calculate the hash of the image (stream) using the hashImplementation.</summary>
+        /// <param name="hashImplementation">HashImplementation to calculate the hash.</param>
+        /// <param name="stream">Stream should 'contain' raw image data.</param>
+        /// <param name="cancellationToken">Cancellation token.</param>
+        /// <returns>hash value.</returns>
+        /// <exception cref="ArgumentNullException">Thrown when <paramref name="hashImplementation"/> or <paramref name="stream"/> is <c>null</c>.</exception>
+        /// <exception cref="SixLabors.ImageSharp.UnknownImageFormatException">Thrown when stream content cannot be loaded as an image.</exception>
+        public static async Task<ulong> HashAsync(this IImageHash hashImplementation, Stream stream, CancellationToken cancellationToken)
+        {
+            if (hashImplementation == null)
+            {
+                throw new ArgumentNullException(nameof(hashImplementation));
+            }
+
+            if (stream == null)
+            {
+                throw new ArgumentNullException(nameof(stream));
+            }
+
+            using var image = await Image.LoadAsync<Rgba32>(stream, cancellationToken);
+            return hashImplementation.Hash(image);
+        }
     }
 }