Function create_provider_unified 

pub fn create_provider_unified(
    provider_name: &str,
    api_key: Option<String>,
    model: Option<String>,
    base_url: Option<String>,
    prompt_cache: Option<PromptCachingConfig>,
    timeouts: Option<TimeoutsConfig>,
) -> Result<Box<dyn LLMProvider>, LLMError>

Compatibility shim that forwards legacy builder/config callers into the canonical provider factory.