Quick.Cart.Ext v6.7 compatible with PHP 8.3

From May 2024, we offer designs based on the Quick.Cart.Ext v6.7 system adapted to PHP 8.3

Faster, safer and... no additional server fees
(some hostings introduce additional fees for using PHP older than 8.1)

The modified version will now work on both the old PHP 7.2 and the latest PHP 8.1, PHP 8.2, PHP 8.3