applyProxyFromSettings

Map the settings_pack PROXY_* knobs (proxy_type / proxy_hostname / proxy_port / proxy_username / proxy_password) onto NetworkRuntime.proxy, the port of session_impl::update_proxy. proxy_type NONE clears any proxy; SOCKS4/SOCKS5(/_pw)/HTTP(_pw) build the matching ProxyConfig. Empty hostnames leave the proxy untouched (incomplete config).