PISA should compute top hits for task TOP_10_COUNT

[jpountz]

It seems to me that the pisa-0.8.2 engine forces evaluation of all hits with the TOP_10_COUNT task, but it doesn't collect them into a priority queue as I would expect. So there is really no difference between TOP_10_COUNT and TOP_1000_COUNT for pisa at the moment.

Let's make it collect hits into a priority queue?

[MBkkt]

It's also looks like it doesn't compute BM25 at least for TOP_<N>_COUNT OR

https://github.com/quickwit-oss/search-benchmark-game/blob/fee26bac7e98bfe9b3ed2803d953ac6cc4073948/engines/pisa-0.8.2/tools/do_query.cpp#L128C25-L128C76