Gradually relax the NMP staticEval check

Gradually relax the NMP staticEval check as we go to
higher depths.

Use tuned values.

STC
LLR: 2.95 (-2.94,2.94) [0.00,5.00]
Total: 16745 W: 3371 L: 3168 D: 10206

LTC:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 5906 W: 875 L: 736 D: 4295

bench: 8548212

src/search.cpp

@@ -731,7 +731,7 @@ namespace {
     if (   !PvNode
         &&  depth >= 2 * ONE_PLY
         &&  eval >= beta
-        && (ss->staticEval >= beta || depth >= 12 * ONE_PLY)
+        && (ss->staticEval >= beta - 35 * (depth / ONE_PLY - 6) || depth >= 13 * ONE_PLY)
         &&  pos.non_pawn_material(pos.side_to_move()))
     {
         ss->currentMove = MOVE_NULL;