Optimize reflection dependency in SmartEnum List property for performance-sensitive scenarios

[mokarchi]

This PR optimizes the reflection dependency through strategic caching improvements:

SmartFlagEnum Optimization

• Added cached enum options: Introduced static readonly Lazy<List<TEnum>> _enumOptions field to match the efficiency of SmartEnum
• Updated List property: Changed from rebuilding collections via _fromName.Value.Values.ToList().AsReadOnly() to direct cached access
• Eliminated repeated reflection calls: Updated FromValue(), DeserializeValue(), TryFromValue(), and FromValueToString() methods to use cached data instead of calling GetAllOptions() repeatedly

Type-Level Reflection Caching

Enhanced TypeExtensions.GetFieldsOfType<T>() with ConcurrentDictionary<Type, object> caching to prevent repeated reflection operations on the same type across different instances.

Backward Compatibility

• No breaking changes to public APIs
• Maintains full backward compatibility
• Thread-safe implementation preserved

[mokarchi]

@ardalis Could you review this, please?