Epoch processing performance optimizations

After some work on reducing slot processing time, which greatly enhance block processing we still have a big bottleneck on every epoch processing. After some measures I was able to pinpoint the specific part of the code were 95% of the time was taken in the epoch processing execution and it was in a particular zip operation under rewards and penalties calculation as show by the following logs:

This could be found here, but the line was modified to an Enum.zip instead of Stream, to be able to measure the bottleneck.

Something more caught my eyes when following the logs, there were 3 things that could be potential candidates for performance optimizations:

1. I'm not completely sure but as far as the log shows, epoch processing occurs more than once within 3/4 blocks of difference instead of happening once every 32 blocks, there might be something involved related to the triggering of the epoch processing
2. committee prefetch happens more than once nearly at the dame time due to the cache not storing the previous process calculating it in the meantime
3. slot processing recalculates block and state root due to them not being available which apparently just happens near the epoch processing as shown in these logs

This could easily become an umbrella Issue with sub task for tackling the aforementioned discoveries one at a time.

Start in lib/lambda_ethereum_consensus/state_transition/epoch_processing.ex around line 415 and use the reported profiling logs to examine the rewards and penalties zip operation. Then investigate the reported repeated epoch processing, committee prefetching, and block/state root recalculation; done means the selected bottleneck or subtask has a measured performance improvement.