Merge commit 'c8213ba0d047569141ed58f5eb86579d976b5614' into cluster

As part of this work, we needed to rename the namespace Stockfish::Cluster
to Stockfish::Distributed, as Cluster is now a type name.

src/perft.h

@@ -51,7 +51,7 @@ uint64_t perft(Position& pos, Depth depth) {
             nodes += cnt;
             pos.undo_move(m);
         }
-        if (Root && Cluster::is_root())
+        if (Root && Distributed::is_root())
             sync_cout << UCIEngine::move(m, pos.is_chess960()) << ": " << cnt << sync_endl;
     }
     return nodes;