Use node counting to early stop search

This introduces a form of node counting which can
be used to further tweak the usage of our search
time.
The current approach stops the search when almost
all nodes are searched on a single move.

The idea originally came from Koivisto, but the
implemention is a bit different, Koivisto scales
the optimal time by the nodes effort and then
determines if the search should be stopped.
We just scale down the `totalTime` and stop the
search if we exceed it and the effort is large
enough.

Passed STC:
https://tests.stockfishchess.org/tests/view/65c8e0661d8e83c78bfcd5ec
LLR: 2.97 (-2.94,2.94) <0.00,2.00>
Total: 88672 W: 22907 L: 22512 D: 43253
Ptnml(0-2): 310, 10163, 23041, 10466, 356

Passed LTC:
https://tests.stockfishchess.org/tests/view/65ca632b1d8e83c78bfcf554
LLR: 2.95 (-2.94,2.94) <0.50,2.50>
Total: 170856 W: 42910 L: 42320 D: 85626
Ptnml(0-2): 104, 18337, 47960, 18919, 108

closes https://github.com/official-stockfish/Stockfish/pull/5053

Bench: 1198939

src/search.h

@@ -219,6 +219,8 @@ class Worker {
         return static_cast<SearchManager*>(manager.get());
     }
 
+    std::array<std::array<uint64_t, SQUARE_NB>, SQUARE_NB> effort;
+
     LimitsType limits;
 
     size_t                pvIdx, pvLast;