def make_bytes(s: str) -> bytes:
    """Helper function to convert a string of digits into packed bytes.

    Ignores any characters other than 0 and 1, in particular whitespace. The
    bits are packed in little-endian order within each byte.
    """
    buf = []
    byte = 0
    idx = 0
    for c in s:
        if c == '0':
            pass
        elif c == '1':
            byte |= 1 << idx
        else:
            # coverage: ignore
            continue
        idx += 1
        if idx == 8:
            buf.append(byte)
            byte = 0
            idx = 0
    if idx:
        buf.append(byte)
    return bytearray(buf)