Renamed getActiveValidators to getActiveValidatorsLoadedInBrain for clarity
By using a Set, the inclusion check validatorIndexesSet.has(validator_index) will be much faster than using an array's .includes() method, especially as the number of validators grows. In this case, transforming validatorIndexes to a Set is okay because all validators index are unique.
getActiveValidatorstogetActiveValidatorsLoadedInBrainfor clarity