Function create_model_provider_for_alias_with_url 

pub fn create_model_provider_for_alias_with_url(
    config: &Config,
    family: &str,
    alias: &str,
    api_key: Option<&str>,
    api_url: Option<&str>,
    options: &ModelProviderRuntimeOptions,
) -> Result<Box<dyn ModelProvider>>

Factory: create model_provider with alias context AND custom base URL.