fix: resolve Checkstyle violations in StringRotation and test

Author: konduri-lakshmi-prasanna

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

@@ -2,6 +2,10 @@
 
 public class StringRotation {
 
+    private StringRotation() {
+        throw new UnsupportedOperationException("Utility class");
+    }
+
     /**
      * Checks if str2 is a rotation of str1
      * @param str1 Original string

src/test/java/com/thealgorithms/strings/StringRotationTest.java

@@ -1,6 +1,7 @@
 package com.thealgorithms.strings;
 
-import static org.junit.jupiter.api.Assertions.*;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import org.junit.jupiter.api.Test;