feat(DocSignedNotification): replace Annotations with PsPdfKitAnnotation in DocSignedNotification

- Introduced new record `PsPdfKitAnnotation` to encapsulate both Instant and Structured annotation data
- Updated `DocSignedNotification` to use `PsPdfKitAnnotation` instead of `ExpandoObject Annotations`
- Modified extension methods to accept and map `PsPdfKitAnnotation`
- Added reference to `EnvelopeGenerator.Application.Annotations.Commands` for `CreateAnnotationCommand`

EnvelopeGenerator.Application/Common/Notifications/DocSigned/Handlers/DocStatusHandler.cs

@@ -33,7 +33,7 @@ public class DocStatusHandler : INotificationHandler<DocSignedNotification>
         {
             Envelope = new() { Id = notification.EnvelopeId },
             Receiver = new() { Id = notification.ReceiverId},
-            Value = JsonSerializer.Serialize(notification.Annotations, Format.Json.ForAnnotations)
+            Value = JsonSerializer.Serialize(notification.PsPdfKitAnnotation.Instant, Format.Json.ForAnnotations)
         }, cancel);
     }
 }