⚖️ Passed pawns: bonus for not enemy pieces ahead

[eduherminio]

Replace miscalculated penalty for blocked passers (#998) with a bonus for unblocked passers, defining unblocked as no enemy pieces in the passed pawn mask of the square where the pawn is.

Score of Lynx-eval-passed-pawns-enemy-ahead-3863-win-x64 vs Lynx 3862 - main: 5859 - 5580 - 8486  [0.507] 19925
...      Lynx-eval-passed-pawns-enemy-ahead-3863-win-x64 playing White: 4324 - 1444 - 4194  [0.645] 9962
...      Lynx-eval-passed-pawns-enemy-ahead-3863-win-x64 playing Black: 1535 - 4136 - 4292  [0.369] 9963
...      White vs Black: 8460 - 2979 - 8486  [0.638] 19925
Elo difference: 4.9 +/- 3.7, LOS: 99.5 %, DrawRatio: 42.6 %
SPRT: llr 2.9 (100.4%), lbound -2.25, ubound 2.89 - H1 was accepted