As in the previous commit, if a command gets doubly applied due to
`commit_status_unknown`, this will could lead to hard-to-debug failures;
one of them was the test hanging because we would never call
`_done.set_value()` in `state_machine::apply` due to `_seen`
overshooting `_apply_entries`.
Fix the problem and print a warning if we apply too many commands.
Fixes: #14072
2fea2fc19c