Function build_url 

pub fn build_url(
    base: &Url,
    path: &str,
    params: &HashMap<String, String>,
    query: &IndexMap<String, QueryValue>,
) -> Result<BuiltUrl, Error>

Build a request URL from base URL, path template, params, and query.

Query keys are serialized in insertion order (IndexMap). A ?foo=bar suffix on path is merged first; explicit query entries override embedded keys.