Enable cache statistics for NioPool

cdstar-backend-nio/src/main/java/de/gwdg/cdstar/pool/nio/NioPool.java

@@ -101,6 +101,7 @@ public class NioPool implements StoragePool {
 			.maximumSize(cacheSize)
 			// Allow GC to shrink the heap during idle hours.
 			.expireAfterAccess(60, TimeUnit.SECONDS)
+			.recordStats() // This has a (small) performance impact
 			.build(this::loadFromDisk);
 	}