Make Resetting the Aspiration Window after FailLow more aggressive

Sets beta=(3alpha+beta)/4 when failLow. Before it was beta=(alpha+beta)/2, even
though in theory we should be getting an upper bound from a failLow, we can’t
trust the score that caused the failLow. Therefore beta=alpha doesn’t work. I
made the buffer between the new beta to the bestValue that caused the failLow
smaller.

passed STC:
https://tests.stockfishchess.org/tests/view/688674947b562f5f7b7315b5
LLR: 2.93 (-2.94,2.94) <0.00,2.00>
Total: 119616 W: 31253 L: 30818 D: 57545
Ptnml(0-2): 313, 14028, 30724, 14397, 346

passed LTC:
https://tests.stockfishchess.org/tests/view/6887e0ad7b562f5f7b731afc
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 96978 W: 24905 L: 24466 D: 47607
Ptnml(0-2): 59, 10376, 27183, 10809, 62

closes https://github.com/official-stockfish/Stockfish/pull/6197

bench: 3085519

AUTHORS

@@ -57,6 +57,7 @@ Ciekce
 clefrks
 Clemens L. (rn5f107s2)
 Cody Ho (aesrentai)
+CSTENTOR
 Dale Weiler (graphitemaster)
 Daniel Axtens (daxtens)
 Daniel Dugovic (ddugovic)

src/search.cpp

@@ -371,7 +371,7 @@ void Search::Worker::iterative_deepening() {
                 // otherwise exit the loop.
                 if (bestValue <= alpha)
                 {
-                    beta  = (alpha + beta) / 2;
+                    beta  = (3 * alpha + beta) / 4;
                     alpha = std::max(bestValue - delta, -VALUE_INFINITE);
 
                     failedHighCnt = 0;