search: enrich lucky search suggestions

Created by: rvantonder

lucky search currently notifies the user of alternative queries that ran, even when those queries return 0 results. This PR collects the count of results coming from each generated query and only sends the notification if we found results.

Pretty cool! Yes, this needs more bookkeeping overhead but it's so valuable I think it's worth it. The previous state is OK for a small number of suggestions, but as the query generation grows, this is going to get out of hand.

Aside: generated query job cancellation appears to not work, it's supposed to also not notify if we've already sent 500+ results total. I've never seen the context cancelled abort lucky search in this code block locally, and I've tried to force it to. This is a separate issue to investigate and shouldn't block this PR though.

Test plan

Experimental and will add a test, putting up for early review/feedback.