* fork choice fixes, round 3
* introduce checkpoint tracker
* split out fork choice backend that is independent of dag
* correctly update best checkpoint to use for head selection
* correctly consider wall clock when processing attestations
* preload head history only (only one history is loaded from database
anyway)
* love the DAG
* switch to fork choice v2
also remove BlockRef.children
* fix
* remove cruft
* reenable fork choice and fix several issues
* in addForkChoice_v2, the `.error` field would be accessed even when
Result is ok
* remove workaround for invalid block structure in fork choice
* fix `tmpState` being used recursively in callback, causing state
corruption while processing attestation
* fix block callback being called twice per block
* pass state to callback to avoid unnecessary rewinding
* enable head select, fix another bug
* never use `get` without `isOk`
* log nil blockref in case blockref is nil
* add missing error checking
* use correct epoch when updating attestation message
* initial fork-choice refactor
* Add fork_choice test for "no votes"
* Initial test with voting: fix handling of unknown validators and parent blocks
* Fix tiebreak of votes
* Cleanup debugging traces
* Complexify the vote test
* fakeHash use the bigEndian repr of number + fix tiebreak for good
* Stash changes: found critical bug in nimcrypto `==` and var openarray
* Passing fork choice tests with varying votes
* Add FFG fork choice scenario + fork choice to the test suite
* Not sure why lmdb / rocksdb reappeared in rebase
* Add sanity checks to .nimble file + integrate fork choice tests to the test DB and test timing
* Cleanup debugging echos
* nimcrypto fix https://github.com/status-im/nim-beacon-chain/pull/864 as been merged, remove TODO comment
* Turn fork choice exception-free
* Cleanup "result" to ensure early return is properly used
* Add a comment on private/public error code vs Result
* result -> results following https://github.com/status-im/nim-beacon-chain/pull/866
* Address comments:
- raises: [Defect] doesn't work -> TODO
- process_attestation cannot fail
- try/except as expression pending Nim v1.2.0
- cleanup TODOs
* re-enable all sanity checks
* tag no raise for process_attestation
* use raises defect everywhere in fork choice and fix process_attestation test
Jacek Sieka
Mamy Ratsimbazafy