Introduce penalty for weak (=unsupported) pawns.

We add a penalty for each pawn which is not protected by another pawn
of the same color.

Passed both short TC
LLR: 2.96 (-2.94,2.94) [-1.50,4.50]
Total: 12107 W: 2411 L: 2272 D: 7424

And long TC
LLR: 2.96 (-2.94,2.94) [0.00,6.00]
Total: 9204 W: 1605 L: 1458 D: 6141

bench: 7682173
Simplify TT replace strategy

Tested for no-regression with SPRT[-3, 1] at STC
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 32046 W: 6020 L: 5918 D: 20108

No functional change.