feat(fork-choice): implement fork choice spec test #305

GrapeBaBa wants to merge 4 commits intogr/feature/forkchoice-zChainSafe/lodestar-z:gr/feature/forkchoice-zfrom

gr/feature/forkchoice-spec-testsChainSafe/lodestar-z:gr/feature/forkchoice-spec-testsCopy head branch name to clipboard