Create a lazy list representing the character codes (chars) in
Stream. List is a partial list ending in an
attributed variable. Unifying this variable reads the next block of
data. The block is stored with the attribute value such that there is no
need to re-read it.
Unlike the previous version of this predicate this version does not
require a repositionable stream. It does require a buffer size of at
least the maximum number of bytes of a multi-byte sequence (6).