Change implementation of AtomicCyclicIterator so that it works with J…

…S/Native

core/src/main/scala/sttp/client3/testing/AtomicCyclicIterator.scala

@@ -1,21 +1,15 @@
 package sttp.client3.testing
 
 import java.util.concurrent.atomic.AtomicInteger
-import java.util.function.IntUnaryOperator
 import scala.util.{Failure, Success, Try}
 
-final class AtomicCyclicIterator[+T] private(val elements: Seq[T]) {
+final class AtomicCyclicIterator[+T] private (val elements: Seq[T]) {
   private val vector = elements.toVector
-  private val lastIndex = elements.length - 1
+  private val length = elements.length
   private val currentIndex = new AtomicInteger(0)
 
-  private val toNextIndex = new IntUnaryOperator {
-    final override def applyAsInt(i: Int): Int =
-      if (i == lastIndex) 0 else i + 1
-  }
-
   def next(): T = {
-    val index = currentIndex.getAndUpdate(toNextIndex)
+    val index = currentIndex.getAndIncrement % length
     vector(index)
   }
 }