Function save_named_batches 

pub fn save_named_batches(
    entries: &[(&str, &[RecordBatch], &Schema)],
    save_dir: &Path,
) -> Result<SaveMetrics>

Save arbitrary named RecordBatch collections with WAL + atomic write.

Each entry is (name, batches, schema). Creates Parquet files like {save_dir}/{name}.parquet with atomic tmp+rename.

This is the generic version of save() — it works with any Arrow data, not just GitObjectStore namespaces.