fix: use real FileUploadHelper instance in tests instead of mock

- Changed property type from FileUploadHelper&MockObject to FileUploadHelper
- Use \OCP\Server::get(FileUploadHelper::class) to get real instance
- Fixes 'File is too big' test that requires actual validation logic
- All 105 FileServiceTest tests now passing

Signed-off-by: Vitor Mattos <[email protected]>

Author: vitormattos

tests/php/Unit/Service/FileServiceTest.php

@@ -82,7 +82,7 @@ final class FileServiceTest extends \OCA\Libresign\Tests\Unit\TestCase {
 	protected IL10N $l10n;
 	protected EnvelopeService $envelopeService;
 	protected vfsDirectory $tempFolder;
-	protected FileUploadHelper&MockObject $uploadHelper;
+	protected FileUploadHelper $uploadHelper;
 
 	public function setUp(): void {
 		// Disable lazy objects to avoid PHP 8.4 dependency injection issues in tests