* initial immutable validator database factoring
* remove changes from chain_dag: this abstraction properly belongs in beacon_chain_db
* add merging mutable/immutable validator portions; individually test database roundtripping of immutable validators and states-sans-immutable-validators
* update test summaries
* use stew/assign2 instead of Nim assignment
* add reading/writing of immutable validators in chaindag
* remove unused import
* replace chunked k/v store of immutable validators with per-row SQL table storage
* use List instead of HashList
* un-stub some ncli_db code so that it uses
* switch HashArray to array; move BeaconStateNoImmutableValidators from datatypes to beacon_chain_db
* begin only-mutable-part state storage
* uncomment some assigns
* work around https://github.com/nim-lang/Nim/issues/17253
* fix most of the issues/oversights; local sim runs again
* fix test suite by adding missing beaconstate field to copy function
* have ncli bench also store immutable validators
* extract some immutable-validator-specific code from the beacon chain db module
* add more rigorous database state roundtripping, with changing validator sets
* adjust ncli_db to use new schema
* simplify putState/getState by moving all immutable validator accounting into beacon state DB
* remove redundant test case and move code to immutable-beacon-chain module
* more efficient, but still brute-force, mutable+immutable validator merging
* reuse BeaconState in getState
* ensure HashList/HashArray caches are cleared when reusing getState buffers; add ncli_db and a unit test to verify this
* HashList.clear() -> HashList.clearCache()
* only copy incrementally necessary immutable validators
* increase strictness of test cases and fix/work around resulting HashList cache invalidation issues
* remove explanatory scaffolding
* allow for storage of full (with all validators) states for backwards/forwards-compatibility
* adjust DbSeq type usage
* store full, with-validators, state every 64 epochs to enable reverting versions
* reduce memory allocation and intermediate objects in state storage codepath
* eliminate allocation/copying through intermediate BeaconStateNoImmutableValidators objects
* skip benchmarking initial genesis-validator-heavy state store
* always store new-style state and sometimes old-style state
* document intent behind BeaconState/Validator type-punnery
* more accurate failure message on SQLite in-memory database initialization failure
Era files contain 8192 blocks and a state corresponding to the length of
the array holding block roots in the state, meaning that each block is
verifiable using the pubkeys and block roots from the state. Of course,
one would need to know the root of the state as well, which is available
in the first block of the _next_ file - or known from outside.
This PR also adds an implementation to write e2s, e2i and era files, as
well as a python script to inspect them.
All in all, the format is very similar to what goes on in the network
requests meaning it can trivially serve as a backing format for serving
said requests.
Mainnet, up to the first 671k slots, take up 3.5gb - in each era file,
the BeaconState contributes about 9mb at current validator set sizes, up
from ~3mb in the early blocks, for a grand total of ~558mb for the 82 eras
tested - this overhead could potentially be calculated but one would lose
the ability to verify individual blocks (eras could still be verified using
historical roots).
```
-rw-rw-r--. 1 arnetheduck arnetheduck 16 5 mar 11.47 ethereum2-mainnet-00000000-00000001.e2i
-rw-rw-r--. 1 arnetheduck arnetheduck 1,8M 5 mar 11.47 ethereum2-mainnet-00000000-00000001.e2s
-rw-rw-r--. 1 arnetheduck arnetheduck 65K 5 mar 11.47 ethereum2-mainnet-00000001-00000001.e2i
-rw-rw-r--. 1 arnetheduck arnetheduck 18M 5 mar 11.47 ethereum2-mainnet-00000001-00000001.e2s
...
-rw-rw-r--. 1 arnetheduck arnetheduck 65K 5 mar 11.52 ethereum2-mainnet-00000051-00000001.e2i
-rw-rw-r--. 1 arnetheduck arnetheduck 68M 5 mar 11.52 ethereum2-mainnet-00000051-00000001.e2s
-rw-rw-r--. 1 arnetheduck arnetheduck 61K 5 mar 11.11 ethereum2-mainnet-00000052-00000001.e2i
-rw-rw-r--. 1 arnetheduck arnetheduck 62M 5 mar 11.11 ethereum2-mainnet-00000052-00000001.e2s
```
* Deferred DAG and fork choice pruning
* fixup
* Address https://github.com/status-im/nimbus-eth2/pull/2384/files#r589448448, rely only on onSLotEnd for state pruning
* no need to store needPruning in the data structure
* lastPrunePoint is updated in pruning proc
* Split eager and LazyPruning
* enforce pruning in updateHead
Mamy Ratsimbazafy
tersec
Jacek Sieka