Introduced a cryptographic infrastructure for PDF signing and validation using PKCS#11-based hardware security modules (HSMs) or software tokens. Key changes include:
- Added `PdfDigitalSignatureService` for signing PDFs, multi-signature support, and signature validation.
- Implemented `Pkcs11ExternalSigner` and `Pkcs11PdfSigningRsa` for PKCS#11-based signing with DevExpress PDF infrastructure.
- Added utilities like `Pkcs11SessionRunner`, `Pkcs11InteropBootstrap`, and `Pkcs11ToolBridge` for session management, library initialization, and fallback mechanisms.
- Introduced `Pkcs11Options` for managing PKCS#11 configurations.
- Updated project dependencies to include `DevExpress.Document.Processor`, `System.Security.Cryptography.Pkcs`, and `Pkcs11Interop`.
- Enhanced error handling and fallback support for PKCS#11 operations.
These changes enable robust and extensible PDF signing capabilities with detailed signature metadata extraction and validation.
