Drop support for sub-second precision timestamps
Convert the batch table columns to integers, and change the
DatabaseStore timestamp conversion methods to only work on full-second /
integer timestamps. This also affects the serialization of “maxlag
exceeded” command records, so those are changed to truncate to the full
second as well; the upgrade maintenance script does not update any
existing JSON serializations of such command records, since they should
be rare (none exist on Toolforge, and I’ve updated the four timestamps
on my local installation manually).