feat: Add preliminary support for enums

[jmjoy]

This pull request introduces significant changes to the phper project, adding support for PHP enums, improving documentation, and making several internal adjustments to enhance functionality and maintainability.

Enum Support:

• Added a new module phper::enums to provide Rust wrappers for PHP enum functionality, supporting pure enums, integer-backed enums, and string-backed enums.
• Updated phper-build/src/lib.rs to include configuration for phper_enum_supported when PHP version is 8.1 or higher.
• Included documentation on how to register enums in phper-doc/doc/_06_module/_08_register_enum/index.md.
• Modified phper-doc/src/lib.rs to include the new enum registration documentation module.
• Added necessary includes for enums in phper-sys/php_wrapper.c.

Documentation and Configuration:

• Enhanced Cargo.toml to include the sealed crate and updated documentation configurations. [1] [2]
• Enabled conditional compilation attributes for documentation in phper/src/lib.rs.

Internal Adjustments:

• Made several internal structs and functions in phper/src/classes.rs public within the crate for broader usage. [1] [2] [3] [4] [5]
• Included EnumEntity in the phper/src/modules.rs module imports.

[jmjoy]

Solve #161

[frederikbosch]

Fantastic, great work. Thank you.

[frederikbosch]

As I am directly implementing this in my ext-fs-notify library, I am wondering how to construct an enum from the Rust side. I'd like to return it from a method. I can add a docs-PR for that once I know how to do it.

[jmjoy]

As I am directly implementing this in my ext-fs-notify library, I am wondering how to construct an enum from the Rust side. I'd like to return it from a method. I can add a docs-PR for that once I know how to do it.

Your request requires further improvement of the enums API, using the PHP function zend_enum_get_case_cstr. I’ll add support for this later.

[frederikbosch]

That's great. I wish I could you with that, but I am afraid I can't. The knowledge gap I have to bridge is one I cannot make right now. Thanks again for your efforts.

[jmjoy]

That's great. I wish I could you with that, but I am afraid I can't. The knowledge gap I have to bridge is one I cannot make right now. Thanks again for your efforts.

Please refer to https://github.com/phper-framework/phper/blob/master/phper-doc/doc/_06_module/_08_register_enum/index.md#using-enumcase-for-direct-access