feat(DocSignedNotificationExtensions): add PublishSafely extension for DocSignedNotification

- Introduced PublishSafely method to safely publish DocSignedNotification events.
- Added fallback logic to publish RemoveSignatureNotification when publishing fails.
- Added missing using directive for RemoveSignatureNotification namespace.

EnvelopeGenerator.Application/Common/Notifications/DocSigned/DocSignedNotification.cs

@@ -1,6 +1,7 @@
 using EnvelopeGenerator.Application.Common.Dto;
 using EnvelopeGenerator.Application.Common.Dto.EnvelopeReceiver;
 using EnvelopeGenerator.Application.Common.Extensions;
+using EnvelopeGenerator.Application.Common.Notifications.RemoveSignature;
 using EnvelopeGenerator.Domain.Constants;
 using MediatR;
 using System.Dynamic;
@@ -60,4 +61,28 @@ public static class DocSignedNotificationExtensions
     /// <returns></returns>
     public static async Task<DocSignedNotification?> ToDocSignedNotification(this Task<EnvelopeReceiverDto?> dtoTask, PsPdfKitAnnotation psPdfKitAnnotation)
         => await dtoTask is EnvelopeReceiverDto dto ? new(dto) { PsPdfKitAnnotation = psPdfKitAnnotation } : null;
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="publisher"></param>
+    /// <param name="notification"></param>
+    /// <param name="cancel"></param>
+    /// <returns></returns>
+    public static async Task PublishSafely(this IPublisher publisher, DocSignedNotification notification, CancellationToken cancel = default)
+    {
+        try
+        {
+            await publisher.Publish(notification, cancel);
+        }
+        catch (Exception)
+        {
+            await publisher.Publish(new RemoveSignatureNotification()
+            {
+                EnvelopeId = notification.EnvelopeId,
+                ReceiverId = notification.ReceiverId
+            }, cancel);
+            throw;
+        }
+    }
 }