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/search.h

@@ -302,15 +302,14 @@ class Worker {
 
     Tablebases::Config tbConfig;
 
-    // Used by NNUE
-
-    Eval::NNUE::AccumulatorCaches refreshTable;
-
     const OptionsMap&           options;
     ThreadPool&                 threads;
     TranspositionTable&         tt;
     const Eval::NNUE::Networks& networks;
 
+    // Used by NNUE
+    Eval::NNUE::AccumulatorCaches refreshTable;
+
     friend class Stockfish::ThreadPool;
     friend class SearchManager;
 };