Restore NPS output for Perft

Previously it was possible to also get the node counter after running a bench with perft, i.e.
`./stockfish bench 1 1 5 current perft`, caused by a small regression from the uci refactoring.

```
Nodes searched: 4865609

===========================
Total time (ms) : 18
Nodes searched  : 4865609
Nodes/second    : 270311611
````

closes https://github.com/official-stockfish/Stockfish/pull/5188

No functional change

src/engine.h

@@ -26,6 +26,7 @@
 #include <string_view>
 #include <utility>
 #include <vector>
+#include <cstdint>
 
 #include "nnue/network.h"
 #include "position.h"
@@ -33,6 +34,7 @@
 #include "thread.h"
 #include "tt.h"
 #include "ucioption.h"
+#include "syzygy/tbprobe.h"  // for Stockfish::Depth
 
 namespace Stockfish {
 
@@ -45,6 +47,8 @@ class Engine {
     Engine(std::string path = "");
     ~Engine() { wait_for_search_finished(); }
 
+    std::uint64_t perft(const std::string& fen, Depth depth, bool isChess960);
+
     // non blocking call to start searching
     void go(const Search::LimitsType&);
     // non blocking call to stop searching