Function variant_gguf_path 

pub fn variant_gguf_path(
    model_dir: &Path,
    variant_prefix: &str,
    task: &str,
    repo_id: &str,
) -> PathBuf

Variant-aware cache path for multi-task repos (Mitra, TabFM): <model_dir>/<variant>-<task>/<owner>__<name>/model-f32.gguf. Centralizes the format!("mitra-{task}") logic duplicated in CLI + Python.