Tests: Cover allowed options helpers.
Add coverage for add_allowed_options(), remove_allowed_options(), and option_update_filter(). Verify strict option-name matching, duplicate handling, preserved array keys, and updates to the $allowed_options global only when no explicit options are passed. Cover array and non-array values of $new_allowed_options.
Developed in: https://github.com/WordPress/wordpress-develop/pull/14171
Props huzaifaalmesbah.
See #65819.