Create new package peer.http.proxy and move proxy-related package classes there
Don't honor HTTP_PROXY environment variable in web context

The security fix to libwww-perl explains best what's happening:
> SECURITY FIX: If LWP::UserAgent::env_proxy is called in a CGI
> environment, the case-insensitivity when looking for 'http_proxy'
> permits 'HTTP_PROXY' to be found, but this can be trivially set by the
> web client using the 'Proxy:' header. The fix applied is that
> $ENV{HTTP_PROXY} is not longer honored for CGI script

See https://bugs.ruby-lang.org/issues/6546#note-9