Introduce a new `DocumentDetailsDto` record to encapsulate shared document metadata and elements without binary payload. Refactor `DocumentDto` to inherit from `DocumentDetailsDto`, eliminating redundant properties and improving code reuse.
Convert `DocumentDto` from a class to a record for immutability. Add a parameterized constructor to `DocumentDto` for initializing binary data alongside metadata. Update `ByteData` to use the `init` accessor.
These changes enhance maintainability, reduce duplication, and enforce immutability by leveraging C# records and inheritance.
Renamed `SignatureDto` to `DocReceiverElementDto` across the codebase to better reflect its purpose as a DTO for document receiver elements.
Updated all references, including:
- `SignatureController.cs`: Changed `doc.Elements` type to `IEnumerable<DocReceiverElementDto>`.
- `DocumentDto.cs`: Updated `Elements` property type.
- `MappingProfile.cs`: Adjusted mappings for the renamed DTO.
- `IDocumentReceiverElementService.cs` and `DocumentReceiverElementService.cs`: Updated interfaces and services to use the new DTO.
- `TestDocumentReceiverElementController.cs`: Updated generic type parameters.
These changes improve clarity, align naming with the domain model, and ensure consistency throughout the application.
