Mark PsPdfKitAnnotation as obsolete

Added an [Obsolete] attribute to the PsPdfKitAnnotation property
in the DocSignedNotification class, indicating that the PSPDFKit
library is deprecated.

Reorganized using directives in DocumentReceiverElementService.cs
to improve consistency and maintain code readability.

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

@@ -20,6 +20,7 @@ public record DocSignedNotification : INotification, ISendMailNotification
     /// <summary>
     /// The PSPDFKit annotation data.
     /// </summary>
+    [Obsolete("The PSPDFKit library is deprecated.")]
     public PsPdfKitAnnotation? PsPdfKitAnnotation { get; init; }
 
     /// <summary>

EnvelopeGenerator.Application/Services/DocumentReceiverElementService.cs

@@ -1,9 +1,9 @@
 using AutoMapper;
 using DigitalData.Core.Application;
-using EnvelopeGenerator.Domain.Entities;
 using EnvelopeGenerator.Application.Common.Dto;
 using EnvelopeGenerator.Application.Common.Interfaces.Repositories;
 using EnvelopeGenerator.Application.Common.Interfaces.Services;
+using EnvelopeGenerator.Domain.Entities;
 
 namespace EnvelopeGenerator.Application.Services;