Stackalloc and marshal the delivery tag (#19857)

Author: danielmarbach

sdk/servicebus/Azure.Messaging.ServiceBus/src/Amqp/AmqpMessageConverter.cs

@@ -6,7 +6,9 @@
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
+using System.Runtime.InteropServices;
 using System.Runtime.Serialization;
+using System.Text;
 using Azure.Core;
 using Azure.Core.Amqp;
 using Azure.Messaging.ServiceBus.Amqp.Framing;
@@ -360,9 +362,13 @@ public static ServiceBusReceivedMessage AmqpMessageToSBMessage(AmqpMessage amqpM
 
             if (amqpMessage.DeliveryTag.Count == GuidSizeInBytes)
             {
-                var guidBuffer = new byte[GuidSizeInBytes];
-                Buffer.BlockCopy(amqpMessage.DeliveryTag.Array, amqpMessage.DeliveryTag.Offset, guidBuffer, 0, GuidSizeInBytes);
-                sbMessage.LockTokenGuid = new Guid(guidBuffer);
+                Span<byte> guidBytes = stackalloc byte[GuidSizeInBytes];
+                amqpMessage.DeliveryTag.AsSpan().CopyTo(guidBytes);
+                if (!MemoryMarshal.TryRead<Guid>(guidBytes, out var lockTokenGuid))
+                {
+                    lockTokenGuid = new Guid(guidBytes.ToArray());
+                }
+                sbMessage.LockTokenGuid = lockTokenGuid;
             }
 
             amqpMessage.Dispose();