Make staticEval independent of the path

current master can yield different staticEvals depending on the path used to reach the position. The reason for this is that the evaluation after a null move is always assumed to be different by 2 * Eval::Tempo, while this is not the case in the current lazy eval.

This patch restores the consistency on staticEval.

position fen 1k3b1q/pP2p1p1/P1K1P1Pp/7P/2B5/8/8/8 w - - 0 1
moves c4b3 h8g8 b3d5 g8h8 -> -2124
moves c4d5 null           -> -2084

Bench: 5368891

src/evaluate.cpp

@@ -849,7 +849,7 @@ namespace {
     // Early exit if score is high
     Value v = (mg_value(score) + eg_value(score)) / 2;
     if (abs(v) > LazyThreshold)
-       return pos.side_to_move() == WHITE ? v : -v;
+       return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo;
 
     // Main evaluation begins here