feat(strings): Add ReverseStringUsingStack to reverse strings using stack

Author: Dhirajgiri18

src/main/java/com/thealgorithms/strings/ReverseStringUsingStack.java

@@ -3,7 +3,7 @@
 import java.util.Scanner;
 import java.util.Stack;
 
-public class ReverseStringUsingStack {
+public final class ReverseStringUsingStack {
 
     /**
      * Main method to take user input and print the reversed string.
@@ -19,6 +19,10 @@ public static void main(String[] args) {
         System.out.println("Reversed String : " + reverse(str));
         sc.close();
     }
+    // Private constructor to hide implicit public one
+    private ReverseStringUsingStack() {
+        throw new UnsupportedOperationException("Utility class");
+    }
 
     /**
      * Reverses a string using a stack.