RFE - extract proxy username and password from http(s)_proxy environment variables

A common convention for the HTT(PS)_PROXY variable is to be able to embed the username and password in the URL like: http://USERNAME:PASSWORD@proxy.com:PORT

choco doesn't appear to recognize this and ends up prompting for the proxy username and password.

Start by tracing Chocolatey's handling of the HTTP_PROXY and HTTPS_PROXY environment variables; no source file or test is identified in the issue. Check how proxy URLs are parsed and how authentication prompts are triggered. Done means credentials embedded in a proxy URL are recognized without prompting, with behavior verified for the documented URL form.

Written by the indexing model from the issue text.