Improve so-vector performance

[benwtrent]

so_vector can take a very long time to run.

I think we should adjust its behavior to improve the overall performance as we are likely doing too much work.

I propose:

• Consider removing some of scenarios. Remove unnecessary ops for so-vector #1012
• Reducing warmup/iterations for script-score scenarios
• Adjusting recall calculations to store previously calculated recall for filtered results (calculating these on the fly for every benchmark adds up).

This will help our performance testing for dense vectors as a whole.