Optimize attackers_to()

https://tests.stockfishchess.org/tests/view/6782decb6ddf09c0b4b6e1b0
LLR: 2.93 (-2.94,2.94) <0.00,2.00>
Total: 105920 W: 27571 L: 27181 D: 51168
Ptnml(0-2): 284, 10808, 30403, 11164, 301

- If we only need to know if attackers exist we can skip some
  calculations.
- Also calculating slider/magic attackers first is better because the
  double lookup is slow due to memory latency.
- I also included a couple of very minor cleanups in search that
  probably don't warrant their own PR but I can open separately if
  that's better.

closes https://github.com/official-stockfish/Stockfish/pull/5762

No functional change

src/search.cpp

@@ -77,7 +77,7 @@ constexpr int futility_move_count(bool improving, Depth depth) {
     return (3 + depth * depth) / (2 - improving);
 }
 
-int correction_value(const Worker& w, const Position& pos, Stack* ss) {
+int correction_value(const Worker& w, const Position& pos, const Stack* ss) {
     const Color us    = pos.side_to_move();
     const auto  m     = (ss - 1)->currentMove;
     const auto  pcv   = w.pawnCorrectionHistory[us][pawn_structure_index<Correction>(pos)];
@@ -1140,7 +1140,7 @@ moves_loop:  // When in check, search starts here
 
         // Decrease reduction if position is or has been on the PV (~7 Elo)
         if (ss->ttPv)
-            r -= 1024 + (ttData.value > alpha) * 1024 + (ttData.depth >= depth) * 1024;
+            r -= 1024 + ((ttData.value > alpha) + (ttData.depth >= depth)) * 1024;
 
         // Decrease reduction for PvNodes (~0 Elo on STC, ~2 Elo on LTC)
         if (PvNode)
@@ -1423,8 +1423,8 @@ moves_loop:  // When in check, search starts here
         && ((bestValue < ss->staticEval && bestValue < beta)  // negative correction & no fail high
             || (bestValue > ss->staticEval && bestMove)))     // positive correction & no fail low
     {
-        const auto       m             = (ss - 1)->currentMove;
-        static const int nonPawnWeight = 154;
+        const auto    m             = (ss - 1)->currentMove;
+        constexpr int nonPawnWeight = 154;
 
         auto bonus = std::clamp(int(bestValue - ss->staticEval) * depth / 8,
                                 -CORRECTION_HISTORY_LIMIT / 4, CORRECTION_HISTORY_LIMIT / 4);