docs: protected final SlotAssignmentResult ensure0(long key1, long key2) {
          assertValid();
          final long size = size();
          if (size == expansionThreshold()) {
              resizeTo(CapacityUtil.nextCapacity(capacity()));
          }
          long slot = keyHash(key1, key2) & mask();
          while (isSlotAssigned(slot)) {
              if (equal(key1OfSlot(slot), key2OfSlot(slot), key1, key2)) {
                  slotAssignmentResult.setAddress(valueAddrOfSlot(slot));
                  slotAssignmentResult.setNew(false);
                  return slotAssignmentResult;
              }
              slot = (slot + 1) & mask();
          }
          setSize(size + 1);
          putKey(baseAddress, slot, key1, key2);
          slotAssignmentResult.setAddress(valueAddrOfSlot(slot));
          slotAssignmentResult.setNew(true);
          return slotAssignmentResult;
      }