Refactor: Standardize method names across clients

Renamed methods across multiple client classes for consistency,
shortening and aligning naming conventions (e.g., `CheckAttachmentsAsync` → `CheckAsync`, `ValidatePdfAsync` → `ValidateAsync`).

Updated corresponding interfaces, unit tests, and documentation
to reflect the new method names. Standardized method signatures
to support both `Stream` and `byte[]` overloads consistently.

Improved error handling in tests and updated examples in the
README for batch processing and validation scenarios. Enhanced
API endpoint overview for clarity.

DocumentService.Client/Clients/SwissQrCodeClient.cs

@@ -12,7 +12,7 @@ namespace DocumentService.Client.Clients;
 public class SwissQrCodeClient(HttpClient httpClient, ILogger<SwissQrCodeClient> logger) : BaseDocumentClient(httpClient, logger), ISwissQrCodeClient
 {
     /// <inheritdoc />
-    public async Task<SwissQrCodeExtractionResult> ExtractSwissQrCodeAsync(Stream pdfStream, bool raw = false, CancellationToken cancellationToken = default)
+    public async Task<SwissQrCodeExtractionResult> ExtractAsync(Stream pdfStream, bool raw = false, CancellationToken cancellationToken = default)
     {
         var endpoint = $"/api/pdf/qr-code/extract-swiss?raw={raw}";
 
@@ -26,7 +26,7 @@ public class SwissQrCodeClient(HttpClient httpClient, ILogger<SwissQrCodeClient>
     }
 
     /// <inheritdoc />
-    public async Task<SwissQrCodeExtractionResult> ExtractSwissQrCodeAsync(byte[] pdfBytes, bool raw = false, CancellationToken cancellationToken = default)
+    public async Task<SwissQrCodeExtractionResult> ExtractAsync(byte[] pdfBytes, bool raw = false, CancellationToken cancellationToken = default)
     {
         var endpoint = $"/api/pdf/qr-code/extract-swiss?raw={raw}";