Implement EnumMetadataGenerator and Registry; remove EnumHelper class

[shibayan]

This pull request introduces a new source generator for enum metadata and refactors how enum values and their display names are handled throughout the codebase. The main improvement is replacing runtime reflection-based enum metadata extraction with a compile-time approach, improving performance and maintainability. It also updates the option classes to utilize the new registry for enum display names and ordering.

Enum metadata generation and registration:

• Added the EnumMetadataGenerator source generator, which analyzes enum declarations at compile time and generates code to register their values and display names in EnumMetadataRegistry. This eliminates the need for runtime reflection and manual ordering.
• Introduced the EnumMetadataRegistry static class, which stores enum metadata and provides methods for registering and retrieving enum values and their display names.

Removal of legacy reflection-based code:

• Removed the EnumHelper<TEnum> class, which previously used reflection to extract enum metadata at runtime. This is now handled by the source generator and registry.

Integration with option classes:

• Updated SelectOptions<T> and MultiSelectOptions<T> to use EnumMetadataRegistry for retrieving enum values and display names, replacing the old reflection-based approach. [1] [2]

Cleanup:

• Removed unnecessary using Sharprompt.Internal; statements from files after eliminating the EnumHelper dependency. [1] [2]