Partitioned Search and Multithreaded solving need to report an accurate score calculation speed (by collecting it from the child threads)

13:37:02.589 [l-2-thread-1] INFO Partitioned Search phase (0) ended: time spent (5443), best score (0hard/-2083610soft), score calculation speed (16/sec), step total (89), partCount (4), runnablePartThreadLimit (6).

Yea right, 16 scores per second, that's a lie.