Clash with drupal/countdown

Problem/Motivation

The module uses the wrong naming for the hook_theme, countdown_theme instead of countdown_clock_theme

Steps to reproduce

composer require drupal/countdown
drush en countdown
PHP Fatal error:  Cannot redeclare countdown_theme() (previously declared in /project/app/public/modules/contrib/countdown_clock/countdown_clock.module:44) in /project/app/public/modules/contrib/countdown/countdown.module on line 42

Proposed resolution

Fix the hook