Revise guidance about when to use compact lists

[julian-cable]

With EPUB, line breaks can occur in different places, so it is no longer feasible to advise using compact format for lists whose items are no more than one line long.

Short list items should still use compact format, although the guidance should now be expressed in a more general form.

Discussion: https://redhat-internal.slack.com/archives/C06N8F87YKZ/p1755590958563129?thread_ts=1755590908.463419&cid=C06N8F87YKZ