Function build_proxy_connector 

pub fn build_proxy_connector(
    config: &ProxyConfig,
) -> Result<ProxyAwareConnector, HttpStackError>

Build a full connector from ProxyConfig.

• Disabled → still returns a ProxyConnector, but with no entries; match_proxy always returns None, behaving equivalently to “no proxy”.
• FromEnv → reads HTTP_PROXY / HTTPS_PROXY / NO_PROXY (case-insensitive, lowercase preferred, matching curl conventions).
• Explicit → uses the given values directly.

Errors

Returns an error if loading native TLS roots fails, or if a proxy URL from the environment cannot be parsed.