notification cooldown appears to not be enforced

[GRarer]

Now that we've deployed the service and I've been using on my phone for about a day, I've noticed that I seem to be getting Boop reminders more than once in a 4-hour period, which isn't supposed to happen.

[GRarer]

in retrospect it's pretty clear why this bug happens. here's CTE where we match selected users with the array of friends who we could pair them with:

friend_options AS (
        SELECT user_a, array_agg(user_b order by random()) as user_bs
        FROM friends_chosen_users join friends on friends_chosen_users.user_uuid = friends.user_a
        group by user_a
    ),

friends_chosen_users won't include anybody who got a notification in the last 4 hours, but we don't guarantee that the second user isn't still cooling down.

fixing this should be easy to implement, but a bit tricky to difficult to test and deploy.