Fix missing initialization of AccumulatorCaches in Eval::trace

Add a constructor to `AccumulatorCaches` instead of just calling
`clear(networks)` to prevent similar issues from appearing in the
future.

fixes https://github.com/official-stockfish/Stockfish/issues/5190

closes https://github.com/official-stockfish/Stockfish/pull/5191

No functional change

src/nnue/nnue_accumulator.h

@@ -50,6 +50,11 @@ struct alignas(CacheLineSize) Accumulator {
 // is commonly referred to as "Finny Tables".
 struct AccumulatorCaches {
 
+    template<typename Networks>
+    AccumulatorCaches(const Networks& networks) {
+        clear(networks);
+    }
+
     template<IndexType Size>
     struct alignas(CacheLineSize) Cache {