Decode a string of bytes as a ByteArray.
Also note that this will eagerly copy the content out of the input to
ensure that the input does not leak in the event that the
ByteArray is live but not forced.
Attempt to decode a token for the length of a finite, known list, or
an indefinite list. If Nothing is returned, then an indefinite
length list occurs afterwords. If Just x is returned,
then a list of length x is encoded.