fix: add private constructor to hide utility class constructor in TopologicalSort

Author: Saipatnaik-23

src/main/java/com/thealgorithms/graphsearch/TopologicalSort.java

@@ -13,7 +13,7 @@
 public class TopologicalSort {
 
     // Private constructor to prevent instantiation
-    private TopologicalSort(){
+    private TopologicalSort() {
         throw new UnsupportedOperationException("This is a utility class and cannot be instantiated");
     }
     /**