* early exit `commonAncestor` when comparing with `finalizedHead`
As all `BlockRef` lead to `finalizedHead` (`parent == nil`),
can shortcut in that situation and immediately return `finalizedHead`
if passed as one of the arguments.
* typo in comment
* add test from #5152
Co-authored-by: tersec <tersec@users.noreply.github.com>
* add note about test complexity
* regenerate test summary
---------
Co-authored-by: tersec <tersec@users.noreply.github.com>
5115aaedb7