Cache small net w/ psqtOnly support

Caching the small net in the same way as the big net allows them to
share the same code path and completely removes
update_accumulator_refresh().

STC:
https://tests.stockfishchess.org/tests/view/662bfb5ed46f72253dcfed85
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 151712 W: 39252 L: 39158 D: 73302
Ptnml(0-2): 565, 17474, 39683, 17570, 564

closes https://github.com/official-stockfish/Stockfish/pull/5194

Bench: 1836777

src/evaluate.cpp

@@ -60,7 +60,7 @@ Value Eval::evaluate(const Eval::NNUE::Networks&    networks,
     int  nnueComplexity;
     int  v;
 
-    Value nnue = smallNet ? networks.small.evaluate(pos, nullptr, true, &nnueComplexity, psqtOnly)
+    Value nnue = smallNet ? networks.small.evaluate(pos, &caches.small, true, &nnueComplexity, psqtOnly)
                           : networks.big.evaluate(pos, &caches.big, true, &nnueComplexity, false);
 
     const auto adjustEval = [&](int optDiv, int nnueDiv, int npmDiv, int pawnCountConstant,