Select less invalidations when we know were archiving segments for a specific period + add total iterations counter to output.
When we're archiving an "All Visits" archive, we know we won't be adding segments to it, so every segment archive we query will be skipped. So it's pointless to query for them all. This PR avoids selecting them so we don't have to go through the loop for them. May provide a visible performance boost in cases where there are many segments for a site.