code: @Override
      public void nextTier() {
          super.nextTier();
          if (it.hashLookupEntryInit())
              hls.initSearchKey(hh.h().hashLookup.key(it.hashLookupEntry));
      }
docs: During iteration, nextTier() is called in doReplaceValue() -> relocation() -> alloc().
  When the entry is relocated to the next tier, an entry should be inserted into hash
  lookup. To insert an entry into hashLookup, should 1) locate empty slot, see {@link
  KeySearch#initKeySearch()}, and 2) know the part of the hash code to insert, we know
  it during iteration