anchorless_list: Make ranges conform to SinglePassRange
anchorless_list: Make ranges conform to SinglePassRange

They were missing const version of iterators as well as iterator and
const_iterator member type aliases.

avikivity/scylla,scylladb/scylla,duarten/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla,duarten/scylla,duarten/scylla,scylladb/scylla