Function prepare_messages_for_provider_cached 

pub async fn prepare_messages_for_provider_cached(
    messages: &[ChatMessage],
    config: &MultimodalConfig,
    cache: &mut LocalImageCache,
) -> Result<PreparedMessages>

Like prepare_messages_for_provider but reuses a LocalImageCache across calls so each unique local image file is read from disk at most once per session (or once per modification for mutable files).