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.Application/Common/DTOs/SwissQrCodeExtractionResult.cs

@@ -32,6 +32,10 @@ namespace DocumentService.Application.Common.DTOs;
 /// }
 /// </example>
 public record SwissQrCodeExtractionResult(
+#if NET
     SwissQrBillDto Bill,
-    IReadOnlyList<string> RawLines
-);
+#else
+    object? Bill,
+#endif
+    IEnumerable<string> RawLines
+);