CARGO: fix passing proxy settings to cargo commands

[kLiHz]

changelog: fix passing proxy-related environment vars to cargo commands

This PR:

• sets up both http_proxy and https_proxy for cargo commands (previously only http_proxy is set, so cargo was not able to proxy https requests);
• it also changes the url scheme to socks for the proxy URI (which is set up as http_proxy and https_proxy env vars' value) when PROXY_TYPE_IS_SOCKS is ture;
• a socks_proxy env var will also be set when PROXY_TYPE_IS_SOCKS.

related issue: #3258

Here's also a naive rust program to check that those env vars are inherited from cargo run command (calling the cargo commands from the rust plugin):

use std::env;

fn main() {
    let keys: [&str; 3] = [
        "http_proxy",
        "https_proxy",
        "socks_proxy",
    ];
    for key in keys {
        match env::var(key) {
            Ok(val) => println!("{key} = {val}"),
            Err(e) => println!("{key} not found. {e}")
        }
    }
}