Tweak time management

Use for adjustment of the falling eval time factor now also the difference
between previous best average score and current best score.

STC:
LLR: 2.95 (-2.94,2.94) <0.00,2.50>
Total: 109216 W: 28296 L: 27900 D: 53020
Ptnml(0-2): 312, 11759, 30148, 11999, 390
https://tests.stockfishchess.org/tests/view/61aafa8d1b31b85bcfa29d9c

LTC:
LLR: 2.93 (-2.94,2.94) <0.50,3.00>
Total: 54096 W: 14091 L: 13787 D: 26218
Ptnml(0-2): 29, 5124, 16447, 5410, 38
https://tests.stockfishchess.org/tests/view/61abbbbd56fcf33bce7d1d64

closes https://github.com/official-stockfish/Stockfish/pull/3833

Bench: 4829419