Reduce big time spikes by reducing PV re-searches.

Save time by reducing PV re-searches above original depth. Instead use 5% extra time on every move.

STC 10+0.1 th 1 :
LLR: 2.93 (-2.94,2.94) {-0.25,1.25}
Total: 90688 W: 9702 L: 9436 D: 71550
Ptnml(0-2): 408, 7252, 29792, 7450, 442
https://tests.stockfishchess.org/tests/view/5f8df807bacb75a4f9a47223

LTC 60+0.6 th 1 :
LLR: 2.97 (-2.94,2.94) {0.25,1.25}
Total: 97856 W: 4602 L: 4303 D: 88951
Ptnml(0-2): 53, 3757, 41057, 3960, 101
https://tests.stockfishchess.org/tests/view/5f8ec4872c92c7fe3a8c602d

closes https://github.com/official-stockfish/Stockfish/pull/3192

Bench 3943959

src/timeman.cpp

@@ -75,7 +75,7 @@ void TimeManagement::init(Search::LimitsType& limits, Color us, int ply) {
   // game time for the current move, so also cap to 20% of available game time.
   if (limits.movestogo == 0)
   {
-      optScale = std::min(0.008 + std::pow(ply + 3.0, 0.5) / 250.0,
+      optScale = std::min(0.0084 + std::pow(ply + 3.0, 0.5) * 0.0042,
                            0.2 * limits.time[us] / double(timeLeft));
       maxScale = std::min(7.0, 4.0 + ply / 12.0);
   }