Make package compliant to new plugin definition

[StefanoMagrassi]

This PR makes the plugin compliant to the new format (ESLint v9) which is supported by defineConfig() utility.

References:

• https://eslint.org/blog/2025/03/flat-config-extends-define-config-global-ignores/#introducing-defineconfig()-for-eslint
• https://eslint.org/docs/latest/extend/plugins#backwards-compatibility-for-legacy-configs

[gabro]

Thanks 🙏