sqlite: PRAGMA optimize on close

sqlite: PRAGMA optimize on close

As recommended by SQLite documentation[1]:

  To achieve the best long-term query performance without the need
  to do a detailed engineering analysis of the application schema
  and SQL, it is recommended that applications run "PRAGMA optimize"
  (with no arguments) just before closing each database connection.

Hopefully that works for our use cases and can make things
faster for us.

[1] https://www.sqlite.org/pragma.html#pragma_optimize