Search tuning at very long time control with new net

Search tuning at very long time control with new net

The most significant change would be the singularBeta formula.
It was first tested by cj5716 (see https://tests.stockfishchess.org/tests/view/647317c9d29264e4cfa74ec7),
and I took much inspiration from that idea.

LTC (fixed games): https://tests.stockfishchess.org/tests/view/6479d8da54dd118e1d990b12
Elo: 0.61 ± 1.2 (95%) LOS: 83.4%
Total: 60000 W: 16278 L: 16172 D: 27550
Ptnml(0-2): 16, 5845, 18179, 5937, 23
nElo: 1.38 ± 2.8 (95%) PairsRatio: 1.02

VLTC 180+1.8: https://tests.stockfishchess.org/tests/view/6479da1454dd118e1d990b2b
LLR: 2.95 (-2.94,2.94) <0.50,2.50>
Total: 33224 W: 9261 L: 8984 D: 14979
Ptnml(0-2): 5, 2809, 10710, 3080, 8

SMP VLTC 8-thread: https://tests.stockfishchess.org/tests/view/647b0fe354dd118e1d992425
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 61398 W: 17386 L: 17081 D: 26931
Ptnml(0-2): 7, 4571, 21232, 4888, 1

closes https://github.com/official-stockfish/Stockfish/pull/4603

Bench: 2805878