Replacing the futility margin static value with a continuous transition
Smooth the futility margin by interpolating the multiplier based on depth, replacing the previous static value with a continuous transition between depth 1 and 10.
Passed STC:
LLR: 2.93 (-2.94,2.94) <0.00,2.00>
Total: 208448 W: 53891 L: 53324 D: 101233
Ptnml(0-2): 629, 24426, 53574, 24939, 656
https://tests.stockfishchess.org/tests/view/69e232206f344a19176002f3
Passed LTC:
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 208938 W: 53432 L: 52765 D: 102741
Ptnml(0-2): 105, 22531, 58550, 23158, 125
https://tests.stockfishchess.org/tests/view/69e8b5d00e9667dd5a7656c6
closes https://github.com/official-stockfish/Stockfish/pull/6780
Bench: 2661424