Tune Fail Low Bonus
Fractional bonus idea is from @Ergodice on
[discord](https://discord.com/channels/435943710472011776/735707599353151579/1244039134499180614).
Values are tuned for 149k games at LTC.
SPSA tune:
https://tests.stockfishchess.org/tests/view/6652d5d5a86388d5e27da9d6
Failed STC:
LLR: -2.95 (-2.94,2.94) <0.00,2.00>
Total: 67424 W: 17364 L: 17528 D: 32532
Ptnml(0-2): 238, 8043, 17299, 7909, 223
https://tests.stockfishchess.org/tests/view/66551e1ba86388d5e27db9f9
Passed LTC:
LLR: 2.94 (-2.94,2.94) <0.00,2.00>
Total: 146910 W: 37141 L: 36695 D: 73074
Ptnml(0-2): 84, 16201, 40441, 16643, 86
https://tests.stockfishchess.org/tests/view/66559949a86388d5e27dcc5d
Passed VLTC:
LLR: 2.95 (-2.94,2.94) <0.50,2.50>
Total: 27248 W: 6924 L: 6633 D: 13691
Ptnml(0-2): 5, 2744, 7835, 3035, 5
https://tests.stockfishchess.org/tests/view/66563f4da86388d5e27dd27a
closes https://github.com/official-stockfish/Stockfish/pull/5299
Bench: 1390709