Fix calculation of hash slots on 32bit env

[acquamarin]

We require the number of hash slots to be power of 2 because we compute the block mask based on that value:

numSlotsPerBlockLog2 = std::log2(numSlotsPerBlock);
 slotIdxInBlockMask =
        common::BitmaskUtils::all1sMaskForLeastSignificantBits(numSlotsPerBlockLog2);