Improve and Expand Documentation for SymmetricEncryptionManager

[Copilot]

This PR adds comprehensive XML documentation to the SymmetricEncryptionManager class, addressing the lack of proper documentation that made it difficult for developers to use the class correctly and safely.

Changes Made

Class-Level Documentation

• Added detailed summary explaining the purpose and security features of SymmetricEncryptionManager
• Documented the underlying AES-256 algorithm with CBC mode and PKCS7 padding
• Included security best practices and important usage notes
• Added a complete, copy-paste-friendly code example showing the full encryption/decryption lifecycle

Method Documentation

• encryptData: Comprehensive documentation including parameter descriptions, security features, password guidelines, and usage examples
• decryptData: Detailed documentation of the decryption process, error handling, and security considerations
• GenerateRandomPassword: Complete documentation of password characteristics, use cases, and security notes

Class and Property Documentation

• EncryptedData: Documented all properties with their cryptographic significance
• EncryptedDataExtensions: Detailed documentation for Base64 conversion methods
• Constants: Explained the purpose and security implications of key sizes and iteration counts

Exception Documentation

All methods now include comprehensive <exception> tags documenting:

• ArgumentException for null/empty passwords
• ArgumentNullException for null encrypted data
• CryptographicException for decryption failures
• FormatException for invalid Base64 strings

Security Documentation

Added extensive security guidance including:

• AES-256 encryption with CBC mode specifications
• PBKDF2-SHA256 key derivation with 100,000 iterations
• Importance of unique salt and IV generation
• Password security recommendations
• Data integrity considerations

The documentation follows XML documentation standards and provides clear, professional guidance for developers using this encryption library.

Fixes #11.

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[Copilot]

Keep only important information in docblocks and put everything else in some markdown file or in the readme

Done! I've refactored the documentation as requested - moved the detailed examples, security practices, and comprehensive guides to the README while keeping only essential information in the XML docblocks. The docblocks now contain just the core information needed for IntelliSense (purpose, parameters, exceptions) while the README has a complete section with examples and best practices. (commit 1ce795f)