def _copy_days_used(orig: dict[str, list[int]]) -> dict[str, list[int]]:
    """
    Return a deep copy of the given dictionary mapping club codes
    to a 0-indexed list of counts of instances per day for that club.
    """
    new = {}
    for (key, inner) in orig.items():
        new[key] = inner[:]
    return new