Optimize the most common update accumalator cases w/o tiling

In the most common case where we only update a single state
it's faster to not use temporary accumulation registers and tiling.
(Also includes a couple of small cleanups.)

passed STC
https://tests.stockfishchess.org/tests/view/651918e3cff46e538ee0023b
LLR: 2.95 (-2.94,2.94) <0.00,2.00>
Total: 34944 W: 8989 L: 8687 D: 17268
Ptnml(0-2): 88, 3743, 9512, 4037, 92

A simpler version
https://tests.stockfishchess.org/tests/view/65190dfacff46e538ee00155
also passed but this version is stronger still
https://tests.stockfishchess.org/tests/view/6519b95fcff46e538ee00fa2

closes https://github.com/official-stockfish/Stockfish/pull/4816

No functional change

src/misc.h

@@ -87,6 +87,7 @@ public:
   void push_back(const T& value) { values_[size_++] = value; }
   const T* begin() const { return values_; }
   const T* end() const { return values_ + size_; }
+  const T& operator[](int index) const { return values_[index]; }
 
 private:
   T values_[MaxSize];