feat: add encrypted JSON casts

[memleakd]

Description

This PR adds encrypted-json and encrypted-json-array casts for Entity properties and Model fields.

This builds on the recently added encrypted cast and adds support for structured values. The values are JSON encoded first, then encrypted before they are stored. When read back, they are decrypted and decoded again.

This is useful when the application needs array/object access in PHP, but encrypted text at rest.

protected array $casts = [
    'settings' => 'encrypted-json-array',
];

encrypted-json returns stdClass, and encrypted-json-array returns arrays. Nullable values can be handled with ?encrypted-json and ?encrypted-json-array.

The implementation reuses the existing JsonCast and EncryptedCast, so this follows the same behavior as the current JSON and encrypted casts. The stored database value is still encrypted text, not queryable JSON.

Tests were added for direct casting, nullable values, invalid payloads, DataConverter, and Entity usage.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value (without duplication)
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide