🔍 Improve RFP return formula: (staticEval + beta)/2

[eduherminio]

Test  | rfp/wise-ciekce
Elo   | 1.12 +- 2.26 (95%)
SPRT  | 8.0+0.08s Threads=1 Hash=32MB
LLR   | -2.26 (-2.25, 2.89) [0.00, 5.00]
Games | N: 55718 W: 17207 L: 17028 D: 21483
Penta | [2102, 6441, 10659, 6490, 2167]
https://openbench.lynx-chess.com/test/148/

> python .\sprt.py -w 17207 -d 21483 -l 17028 -e0 0 -e1 3
ELO: 1.12 +- 2.26 [-1.14, 3.37]
LLR: -0.309 [0.0, 3.0] (-2.94, 2.94
Continue Playing

40+0.4 [0, 3] cancelled, unfortunately

Score of Lynx-rfp-wise-ciekce-2593-win-x64 vs Lynx 2592 - main: 2239 - 2103 - 3638  [0.509] 7980
...      Lynx-rfp-wise-ciekce-2593-win-x64 playing White: 1653 - 557 - 1780  [0.637] 3990
...      Lynx-rfp-wise-ciekce-2593-win-x64 playing Black: 586 - 1546 - 1858  [0.380] 3990
...      White vs Black: 3199 - 1143 - 3638  [0.629] 7980
Elo difference: 5.9 +/- 5.6, LOS: 98.0 %, DrawRatio: 45.6 %
SPRT: llr 1.61 (55.8%), lbound -2.25, ubound 2.89