Simplify time management reduction logic
Simplify the time management reduction logic by replacing the previous sigmoid
function with the linear interpolate function introduced in #6729 , resulting
in a cleaner and more efficient calculation of move stability that avoids
unnecessary exponential operations.
Passed STC non-reg:
LLR: 2.95 (-2.94,2.94) <-1.75,0.25>
Total: 161856 W: 41933 L: 41852 D: 78071
Ptnml(0-2): 418, 18137, 43792, 18108, 473
https://tests.stockfishchess.org/tests/view/69e117a46f344a1917600148
Passed LTC non-reg:
LLR: 2.95 (-2.94,2.94) <-1.75,0.25>
Total: 108726 W: 27819 L: 27692 D: 53215
Ptnml(0-2): 59, 11084, 31942, 11227, 51
https://tests.stockfishchess.org/tests/view/69e563c00e9667dd5a7652ac
This is a follow-up for #6091 #6729
closes https://github.com/official-stockfish/Stockfish/pull/6765
No functional change