Scale Null Move Pruning reduction dynamically based on evaluation margin
This patch introduces a dynamic scaling factor for Null Move Pruning (NMP) reductions. By scaling the reduction depth relative to the static evaluation margin against beta, the engine can afford more aggressive reductions in positions that are overwhelmingly favorable, optimizing CPU cycle utilization without compromising search integrity.
Passed STC:
LLR: 2.94 (-2.94,2.94) <0.00,2.00>
Total: 85504 W: 22383 L: 22000 D: 41121
Ptnml(0-2): 225, 9855, 22218, 10220, 234
https://tests.stockfishchess.org/tests/view/6a4793daf97ff95f78795812
Passed LTC:
LLR: 2.95 (-2.94,2.94) <0.50,2.50>
Total: 205800 W: 53879 L: 53224 D: 98697
Ptnml(0-2): 98, 21747, 58561, 22390, 104
https://tests.stockfishchess.org/tests/view/6a4b864ff97ff95f78795e52
closes https://github.com/official-stockfish/Stockfish/pull/6963
Bench: 2513153