The "AbstractClientTestCase" is missing download testing

[aik099]

The "AbstractClientTestCase" class doesn't have a test that verifies downloading over http/https protocol.

The #232 and #234 are the direct cause of this.

Plan

1. create an URL (e.g. download_attachment.php near the debug_response.php), that once accessed, will return:
   • 303 See Other HTTP code
   • a Location header with a URL (on the same server) where actual downloadable file is located
2. then will use ClientInterface::sendRequest method to access that page and check what's returned
3. if the contents matches the to-be-downloaded file, then test passes
4. initially test should fail for CurlClient, because it doesn't follow location by default

HTTP/1.1 303 See Other
Location: https://www.example.com/other-resource
Content-Type: text/html; charset=UTF-8
Content-Length: 0
Date: Tue, 09 Jan 2025 10:00:00 GMT

[aik099]

Closed via #240.