Updated `MappingProfile` to map `Signature.DataUrl` to
`DocReceiverElement.Ink` using the new `MapDataUrlToRequiredBytes`
extension method. Added `MapDataUrlToRequiredBytes` to handle
base64-encoded data URLs, converting them to byte arrays.
Introduced a `using System;` directive in `AutoMapperAuditingExtensions.cs`
to support `DateTime`. Retained `MapChangedWhen` functionality while
extending mapping capabilities for handling base64 data URLs.