curl_close() deprecation warnings on PHP 8.5+

[etrepat]

Since PHP 8.0, CurlHandle was changed from a resource to an object (CurlHandle), which is automatically garbage collected when it goes out of scope. Starting with PHP 8.5, calling curl_close() explicitly triggers a deprecation notice.

The Client class calls curl_close() explicitly in several places across all public API methods (startSolicitation, getIdentificationForm, updateOrder, ...), producing noisy deprecation warnings on an application running PHP 8.5+.