Replaced `await _mediator.Publish(docSignedNotification, cancel)` with
`await _mediator.PublishSafely(docSignedNotification, cancel)` to ensure
safe publishing of notifications without unhandled exceptions.
- 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`
