fixed currencies not available and insurance limit

[ferroche90]

Title: Implement Insurance Limit Checks and Currency Utility Update

Description: This pull request introduces two updates to the codebase:

1. Insurance Limit Checks for Shipments:

   • Added a protected function check_insurance_amount_limit to validate insurance amounts for EU and non-EU shipments.
   • For non-EU shipments, the insured amount is set to €500 if insurance is selected and the order total exceeds €5000.
   • For EU shipments, an exception is thrown if insurance is selected and the order total exceeds €5000, enforcing the maximum allowed insurance amount.

2. Currency Utility Enhancement:

   • Updated the get_available_currency() function to include all WooCommerce currencies.

Files Changed:

• src/Rest_API/Shipping/Item_Info.php:
  • check_insurance_amount_limit() function implementation.
• src/Utils.php:
  • Pre-definition of essential currencies in get_available_currency().