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/thread.cpp

@@ -24,6 +24,7 @@
 #include <memory>
 #include <unordered_map>
 #include <utility>
+#include <array>
 
 #include "misc.h"
 #include "movegen.h"
@@ -203,6 +204,7 @@ void ThreadPool::start_thinking(const OptionsMap&  options,
         th->worker->rootPos.set(pos.fen(), pos.is_chess960(), &th->worker->rootState);
         th->worker->rootState = setupStates->back();
         th->worker->tbConfig  = tbConfig;
+        th->worker->effort    = {};
     }
 
     main_thread()->start_searching();