Implement OO hooks

We should modernize the hooks implemented in markdown_easy.module as modern OO hooks.

For more info:

1. https://www.drupal.org/node/3442349 →
2. https://www.hashbangcode.com/article/drupal-11-object-oriented-hooks-and...
3. https://www.drupaleasy.com/blogs/ultimike/2024/10/why-drupal-module-deve...