Fix ALA detection for NL and international Shipments

[OlfatProgressus]

All Submissions:

• Does your code follow WooCommerce and WordPress standards?
• Have you successfully run tests with your changes locally?
• Have you tested both blocks/non-blocks cart/checkout?
• Have you tested the cart and checkout as both a logged-in user and a guest?
• Have you successfully placed an order as both a logged-in user and a guest?
• Did you have the query monitor plugin active during all testing?

Changes proposed in this Pull Request:

Closes # .
Task url

How to test the changes in this Pull Request:

1. Place order with Belgium address and eligible for letterbox product
2. Add same product to cart and go to the checkout page again
3. change the country to Netherland, you shouldn’t see the delivery days menu now, if the address is correct you should see "These items are eligible for letterbox delivery."
4. when back to Belgium, you should see the delivery days menu

Other information:

• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changelog entry

Enter a summary of all changes on this Pull Request. This will appear in the changelog if accepted.

[Abdalsalaam]

LGTM, can you check the comment I added? and also please add a changelog
thanks

[Abdalsalaam]

I think adding is_letterbox to the early-exit responses (lines 343-351, 365-373 of Extend_Block_Core.php) is better than this, so the frontend always gets an explicit letterbox signal