genesisBuilder performance

[dapplion]

Describe the bug

genesisBuilder does some quite inefficient things:

• Recompute the list of active validators for every batch of deposits:

  lodestar/packages/beacon-state-transition/src/util/genesis.ts

  Line 35 in 00a6ffa

  export function isValidGenesisValidators(config: IChainForkConfig, state: allForks.BeaconState): boolean {

• Re-hash the state every time deposits are applied

  lodestar/packages/beacon-state-transition/src/util/genesis.ts

  Line 178 in 00a6ffa

  state.genesisValidatorsRoot = config

• Verify deposit signatures in the multi-thread runner, to both speed it up and unfreeze the main thread

Expected behavior

Optimize items listed above

[dapplion]

Review if it was fixed by #3760

[dapplion]

No longer relevant since no network goes through genesis generation