Speed up TT store by checking for matches first

Pure speed improvement to TranspositionTable::store()

The new code first checks all four slots in the TTEntry for an empty or matching slot, in order to avoid slower "replace strategy" code completely in those cases. The loop is also unrolled (a measurable speed improvement) to the constant ClusterSize of 4. The loop that implements the replace strategy only needs to execute 3 times instead of the original 4. In the old version, replace and tte started off pointing to the same slot which did nothing in the first iteration.

Standard bench shows approximately 1.4% speed improvement on my machine.

No functional change.