* don't write blocks that get added to database
* don't write states
* write to folders
* add state dumping feature to `ncli_db` to get any known state from the
database
* collect signature production and verificaiton in one place
Signatures are made over data and domain - here we collect all such
activities in one place.
Also:
* security: fix cast-before-range-check
* log block/attestation verification consistently
* run block verification based on `getProposer` in its own history
* clean up some unused stuff
* import
* missing raises
* random fixes
* create dump dir on startup
* don't crash on failure to write dump
* fix a few `uint64` instances being used when indexing arrays - this
should be a compile error but isn't due to compiler bugs
* fix standalone test_block_pool compilation
* add signed block processing in ncli
* reuse cache entry instead of allocating a new one
* allow for small clock disparities when validating blocks
* reorder ssz
* split into hash_trees and ssz_serialization, roughly, for hashing and
IO
* move bitseqs into ssz (from stew)
* clean up imports
* docs, imports
* switch state transition caching usage to shuffled active validator indices to match EpochRef
* refactor the EpochRef -> StateCache transformation; elide pointless mapIt
* limit state passed between get_beacon_committee(...) and compute_committee(...)
* tweaks
* plumbing between block pool and state transition functions around active validator indices and committees
* have shared epochrefs followed by blockref tree while allowing for skipped slots
* factor out the epoch info extraction; document how the EpochRef follows forks