Refactor accumulator storage/updates

Passed Non-regression STC:
LLR: 2.93 (-2.94,2.94) <-1.75,0.25>
Total: 115840 W: 29983 L: 29854 D: 56003
Ptnml(0-2): 338, 12990, 31149, 13091, 352
https://tests.stockfishchess.org/tests/view/67d0a044166a3e8781d84223

closes https://github.com/official-stockfish/Stockfish/pull/5927

No functional change

src/nnue/network.h

@@ -29,13 +29,16 @@
 #include <utility>
 
 #include "../memory.h"
-#include "../position.h"
 #include "../types.h"
 #include "nnue_accumulator.h"
 #include "nnue_architecture.h"
 #include "nnue_feature_transformer.h"
 #include "nnue_misc.h"
 
+namespace Stockfish {
+class Position;
+}
+
 namespace Stockfish::Eval::NNUE {
 
 enum class EmbeddedNNUEType {
@@ -64,11 +67,13 @@ class Network {
     bool save(const std::optional<std::string>& filename) const;
 
     NetworkOutput evaluate(const Position&                         pos,
+                           AccumulatorStack&                       accumulatorStack,
                            AccumulatorCaches::Cache<FTDimensions>* cache) const;
 
 
     void verify(std::string evalfilePath, const std::function<void(std::string_view)>&) const;
     NnueEvalTrace trace_evaluate(const Position&                         pos,
+                                 AccumulatorStack&                       accumulatorStack,
                                  AccumulatorCaches::Cache<FTDimensions>* cache) const;
 
    private:
@@ -100,16 +105,18 @@ class Network {
 
     template<IndexType Size>
     friend struct AccumulatorCaches::Cache;
+
+    friend class AccumulatorStack;
 };
 
 // Definitions of the network types
 using SmallFeatureTransformer =
-  FeatureTransformer<TransformedFeatureDimensionsSmall, &StateInfo::accumulatorSmall>;
+  FeatureTransformer<TransformedFeatureDimensionsSmall, &AccumulatorState::accumulatorSmall>;
 using SmallNetworkArchitecture =
   NetworkArchitecture<TransformedFeatureDimensionsSmall, L2Small, L3Small>;
 
 using BigFeatureTransformer =
-  FeatureTransformer<TransformedFeatureDimensionsBig, &StateInfo::accumulatorBig>;
+  FeatureTransformer<TransformedFeatureDimensionsBig, &AccumulatorState::accumulatorBig>;
 using BigNetworkArchitecture = NetworkArchitecture<TransformedFeatureDimensionsBig, L2Big, L3Big>;
 
 using NetworkBig   = Network<BigNetworkArchitecture, BigFeatureTransformer>;