backport optimistic knn query execution to 10x

[msokolov]

Description

I had intended to do this after letting it bake on main, but forgot to do so. #14226 was the main change, but I think there were a couple of followup patches and/or test fixes that also need to be backported. We also need to check if there are any changes to public APIs. I don't think there were, but it's been a couple of months now ...

[msokolov]

Yes I think we also need #14680 and #14640 and bb3c7c7

[msokolov]

OK, this looks safe from an API perspective; no public API changes, just a new implementation in AbstractKnnVectorQuery. I'll go ahead and push.