Add Swiss QR Code extraction feature

Introduced DTOs for request and response to handle Swiss QR Code extraction from PDF documents. Implemented `ExtractSwissQrCodeHandler` to process the extraction using `ISwissQrCodeProcessor`. Added validation for the query with `ExtractSwissQrCodeValidator`. Developed unit tests to ensure correct behavior for successful and failure scenarios.

DocumentOperator.Application/Common/DTOs/ExtractSwissQrCodeRequest.cs

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+namespace DocumentOperator.Application.Common.DTOs;
+
+/// <summary>
+/// Request to extract Swiss QR Code from a PDF document.
+/// The QR code must be located on the last page of the document.
+/// </summary>
+/// <param name="References">Array of reference strings to pass through in the response</param>
+/// <param name="Base64Pdf">PDF document encoded as Base64 string</param>
+public record ExtractSwissQrCodeRequest(
+    IReadOnlyList<string> References,
+    string Base64Pdf
+);

DocumentOperator.Application/Common/DTOs/ExtractSwissQrCodeResponse.cs

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+namespace DocumentOperator.Application.Common.DTOs;
+
+/// <summary>
+/// Response containing extracted Swiss QR Code data and passed-through references.
+/// </summary>
+/// <param name="References">Reference strings passed through from the request</param>
+/// <param name="QrCodeData">Parsed Swiss QR Code data from the last page of the PDF</param>
+public record ExtractSwissQrCodeResponse(
+    IReadOnlyList<string> References,
+    SwissQrCodeDataDto QrCodeData
+);
+
+/// <summary>
+/// Swiss QR Code data according to Swiss QR Bill Standard 2.0
+/// </summary>
+public record SwissQrCodeDataDto(
+    string QrType,
+    string Version,
+    string CodingType,
+    string Iban,
+    AddressDataDto Creditor,
+    AddressDataDto? UltimateCreditor,
+    decimal? Amount,
+    string Currency,
+    AddressDataDto? UltimateDebtor,
+    string ReferenceType,
+    string? Reference,
+    string? UnstructuredMessage,
+    string? BillInformation,
+    IReadOnlyList<string>? AlternativeProcedureParameters
+);
+
+/// <summary>
+/// Address data (creditor or debtor) in Swiss QR Code
+/// </summary>
+public record AddressDataDto(
+    string AddressType,
+    string Name,
+    string? Street,
+    string? BuildingNumber,
+    string? AddressLine1,
+    string? AddressLine2,
+    string PostalCode,
+    string City,
+    string Country
+);