docs: def split_pks(cols):
    """Returns a 2-tuple of tuples of ((primary_key_cols), (non_primary_key_cols))."""
    pks = []
    others = []
    for name, col in cols.items():
      if col["is_primary_key"] == "t":
        pks.append(name)
      else:
        others.append(name)
  
    return (tuple(pks), tuple(others))