Optimize block size based on query type

We should benchmark the latency we get from different block sizes as well as how much concurrency we can get from different object stores.

Because of request rate limits, there's likely to be a tradeoff between latency (better with smaller block sizes) and throughput (better with larger block sizes). Depending on the type of query, we may want to optimize for one or the other. For example, a KNN query will likely want to optimize for latency. Whereas a OLAP scan will want to optimize for throughput. We should be able to provide good automatic defaults based on the query plan. Of course, the user can always input their own settings as needed.