Enable pragma busy_timeout in sqlite

[jlewi]

See
https://www.sqlite.org/pragma.html#pragma_busy_timeout

By default sqlite doesn't retry DB operations if the sqlite DB is busy.

In #347 we started observing sqlite busy errors. We should consider enabling pragma busy_timeout. I didn't enable it in #347 because I want see how bad contention is before enabling retries. #347 is fixing a bunch of bugs that I think are contributing to spurious SQLIte busy errors.