Saves us from doing a malloc/free call for every item on the list. ok op@

Instead of internally opening and closing the same commit object over and over again, require callers to pass an open commit object in. Avoids an inherent dependency on the commit object cache for reasonable performance. ok op@

Need for filtering by path sugggested by kn@ ok naddy@

The singly-linked tail queue macros were added to OpenBSD 6.9 and are more widely available on other systems. ok stsp

This will be required by a future 'gotadmin pack' command.

This will be required by a future 'gotadmin pack' command.