Evaluate improvements to fair bots matching

[JustArchi]

Once #1375 is merged, we can evaluate the logic for selecting the bots to match and whether we can come up with something better than the existing of "order by any bots firstly, then stop at 20 empty matches, no more than 40 bots total".

Before bringing in very advanced and complex logic that has no purpose, I'm thinking of something simple - it should be good enough to simply stop trying to match any bots once we hit consecutive 20 empty matches, and then move on to the fair bots. This will allow the user to still prefer any bots and have a priority for them, but once we verify that top 20 any bots offer not a single match for us, we can try top 20 fair bots next. Even if we get one single match with any bot around 10th tried bot, this will still result in 10 more fair users tried if the next 20 bots will have no extra matches for us, which is a very good balance between effectiveness and code complexity.

As usual, discussion welcome until I decide upon something.