Increase see prune depth

This seems good at short TC controls.

After 10000 games at 20+0.05
ELO: 9.56 +-6.8 (95%) LOS: 100.0%
Total: 10000 W: 1949 L: 1674 D: 6377

Testing at long TC and regression testing is still
ongoing. So this is a bit speculative commit and
could be reverted in the future.

Also re-testing at long TC the SEE pruning in PV nodes
seems less effective (perhaps even a regression, but
still ongoing) so disabled for now.

bench: 4968764

src/search.cpp

@@ -852,14 +852,14 @@ namespace {
       newDepth = depth - ONE_PLY + ext;
 
       // Step 13. Futility pruning (is omitted in PV nodes)
-      if (   !captureOrPromotion
+      if (   !PvNode
+          && !captureOrPromotion
           && !inCheck
           && !dangerous
           &&  move != ttMove)
       {
           // Move count based pruning
-          if (   !PvNode
-              && depth < 16 * ONE_PLY
+          if (   depth < 16 * ONE_PLY
               && moveCount >= FutilityMoveCounts[depth]
               && (!threatMove || !refutes(pos, move, threatMove)))
           {
@@ -876,7 +876,7 @@ namespace {
           futilityValue =  ss->staticEval + ss->evalMargin + futility_margin(predictedDepth, moveCount)
                          + Gain[pos.piece_moved(move)][to_sq(move)];
 
-          if (!PvNode && futilityValue < beta)
+          if (futilityValue < beta)
           {
               if (SpNode)
                   splitPoint->mutex.lock();
@@ -885,7 +885,7 @@ namespace {
           }
 
           // Prune moves with negative SEE at low depths
-          if (   predictedDepth < 2 * ONE_PLY
+          if (   predictedDepth < 3 * ONE_PLY
               && pos.see_sign(move) < 0)
           {
               if (SpNode)