v0.33.1 — halve the daily new-item ceiling on archive.org

The ceiling is per day, but what it guards against is a burst: creating roughly a
dozen items inside an hour is what answers 503 SlowDown with 'appears to be
spam'. Ten a day can still be ten inside ten minutes when several repositories'
schedules land together.

It is also counted by querying archive.org rather than by keeping a tally, and
that search index lags by minutes, so the number in flight can exceed the ceiling
before the count catches up. Five leaves margin for both.

Nothing is lost by going slower. An item created a day later is the same item,
and a repository whose tree has not changed uploads nothing at all.