When testing a combination of settings that affect the datadir (e.g. prune, blockfilter, …) we may need a lot of datadirs. Bump the maximum number of nodes proactively from 8 to 12, so that caches get populated with 12 node dirs, as opposed to 8.
Also, add an assert that the list of deterministic keys is exactly the number of max nodes (and not more than that.
Also, create the cache faster.