Pass Unity callback request IDs through iOS

IntegrationTests/Assets/Tests/EditMode/NativeBridgeRequestIdContractTests.cs

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+using System;
+using System.IO;
+using NUnit.Framework;
+using UnityEngine;
+
+public class NativeBridgeRequestIdContractTests
+{
+    [Test]
+    public void IosRequestAwareResponseNormalizesNilRequestId()
+    {
+        var source = File.ReadAllText(
+            Path.Combine(
+                Application.dataPath,
+                "RevenueCat/Plugins/iOS/PurchasesUnityHelper.m"));
+        var helper = ExtractBlock(
+            source,
+            "- (void)sendJSONObject:(nullable NSDictionary *)jsonObject");
+
+        Assert.That(
+            helper,
+            Does.Contain(
+                "response[RCCallbackRequestIdKey] = requestId ?: @\"\";"));
+    }
+
+    private static string ExtractBlock(string source, string marker)
+    {
+        var markerIndex = source.IndexOf(marker, StringComparison.Ordinal);
+        Assert.That(markerIndex, Is.GreaterThanOrEqualTo(0));
+        var openingBrace = source.IndexOf('{', markerIndex);
+        Assert.That(openingBrace, Is.GreaterThanOrEqualTo(0));
+
+        var depth = 0;
+        for (var index = openingBrace; index < source.Length; index++)
+        {
+            if (source[index] == '{')
+            {
+                depth++;
+            }
+            else if (source[index] == '}')
+            {
+                depth--;
+                if (depth == 0)
+                {
+                    return source.Substring(
+                        markerIndex,
+                        index - markerIndex + 1);
+                }
+            }
+        }
+
+        Assert.Fail($"Unclosed block after marker '{marker}'.");
+        return null;
+    }
+}