Function import_csv_from 

pub fn import_csv_from<R: Read>(
    reader: R,
    model: &mut Model,
    spec: &ImportSpec,
) -> Result<usize>

Import CSV/TSV data read from reader into model per spec (spec.path is ignored). Distinct dimension-column values become items, interned by name — an item is reused when one already exists with that name in the target category. Returns the number of cells imported.