Instead of loading one article at-a-time from over.sqlite3, we
can use SQL to mass-load IN (?,?, ...) all results with a single
SQLite query. Despite SQLite being in-process and having no
network latency, the reduction in SQL query executions from
loading multiple rows at once speeds things up significantly.
We'll keep the over->get_art optimizations from the previous
commit, since it still speeds up long-lived responses, slightly.