Refactor DTOs and tests; add framework-specific handling

Refactored the codebase to use shared DTOs from `DocumentService.Application.Common.DTOs`, removing inline DTO definitions in client interfaces and tests. Introduced conditional compilation to handle framework-specific differences in DTOs and handlers.

Updated test cases to align with the new DTO structures, including `SwissQrCodeExtractionResult`, `PdfValidationResult`, and `ZugferdExtractionResult`. Adjusted test data to match updated DTO properties.

Cleaned up solution and project files, ensuring proper references and organization. Removed unused files and fixed project references in `DocumentService.Tests.csproj`. Improved maintainability and consistency across the codebase.

DocumentService.Client/Interfaces/ISwissQrCodeClient.cs

@@ -1,3 +1,5 @@
+using DocumentService.Application.Common.DTOs;
+
 namespace DocumentService.Client.Interfaces;
 
 /// <summary>
@@ -24,13 +26,3 @@ public interface ISwissQrCodeClient
     Task<SwissQrCodeExtractionResult> ExtractSwissQrCodeAsync(byte[] pdfBytes, bool raw = false, CancellationToken cancellationToken = default);
 }
 
-/// <summary>
-/// DTO for Swiss QR Code extraction result
-/// </summary>
-public record SwissQrCodeExtractionResult
-{
-    /// <summary>Parsed Swiss QR bill object. <c>null</c> when <c>raw=true</c> was requested.</summary>
-    public object? Bill { get; init; }
-    /// <summary>Raw QR code text lines. Populated when <c>raw=true</c> was requested.</summary>
-    public List<string> RawLines { get; init; } = new();
-}