* 60% state replay speedup
* don't use HashList for epoch participation - in addition to the code
currently clearing the caches several times redundantly, clearing has to
be done each block nullifying the benefit (35%)
* introduce active balance cache - computing it is slow due to cache
unfriendliness in the random access pattern and bounds checking and we
do it for every block - this cache follows the same update pattern as
the active validator index cache (20%)
* avoid recomputing base reward several times per attestation (5%)
Applying 1024 blocks goes from 20s to ~8s on my laptop - these kinds of
requests happen on historical REST queries but also whenever there's a
reorg.
* fix test and diffs
7501f10587