Update plugin for WooCommerce block-based checkout compatibility

[ouun]

We need to update the plugin so that the additional checkbox we register is also added to block-based WooCommerce checkouts in the latest WooCommerce versions (8.3+). This includes:

• Registering the checkbox using the Checkout Block’s extensibility API (JavaScript Slot/Fill system).
• Ensuring the checkbox still works for classic checkout for backward compatibility.
• Handling data submission and validation in both checkout flows.

This is a reminder to work on implementing this compatibility update.

See: https://developer.woocommerce.com/docs/block-development/cart-and-checkout-blocks/additional-checkout-fields/#rendering-a-checkbox-field