Fix C# 9.0 Compilation Errors (#548)

* auto-claude: subtask-1-1 - Convert record struct to struct

Convert record struct declarations to regular struct declarations to fix
CS8773 compilation errors. Record struct is a C# 10 feature that may not
be available in the target C# version.

Changes:
- JActionTask.cs: internal record struct -> internal struct
- JActionRunner.cs: private record struct JActionUpdate -> private struct
- JActionAwaitable.cs: public readonly record struct -> public readonly struct
  with explicit fields and constructors for JActionAwaitable and JActionAwaiter

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* auto-claude: subtask-1-2 - Wrap TestRunnerCallbacks.cs in #if UNITY_INCLUDE_TESTS

Wrapped entire TestRunnerCallbacks.cs file in conditional compilation
directive to fix CS0234/CS0246 errors when Unity Test Framework is not
included in the project.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: JasonXuDeveloper

UnityProject/Packages/com.jasonxudeveloper.jengine.core/Editor/Misc/TestRunnerCallbacks.cs

@@ -1,3 +1,4 @@
+#if UNITY_INCLUDE_TESTS
 using UnityEditor;
 using UnityEditor.TestTools.TestRunner.Api;
 using UnityEngine;
@@ -73,3 +74,4 @@ public void TestStarted(ITestAdaptor test) { }
         public void TestFinished(ITestResultAdaptor result) { }
     }
 }
+#endif

UnityProject/Packages/com.jasonxudeveloper.jengine.util/Runtime/Internal/JActionRunner.cs

@@ -41,7 +41,7 @@ internal static class JActionRunner
         /// <summary>
         /// Marker struct for identifying our update in the PlayerLoop.
         /// </summary>
-        private record struct JActionUpdate;
+        private struct JActionUpdate { }
 
 #if UNITY_EDITOR
         [InitializeOnLoadMethod]

UnityProject/Packages/com.jasonxudeveloper.jengine.util/Runtime/Internal/JActionTask.cs

@@ -41,7 +41,7 @@ internal enum JActionTaskType : byte
     /// This struct is designed for minimal memory footprint and efficient execution.
     /// State is stored externally via <see cref="IStateStorage"/> to avoid boxing value types.
     /// </remarks>
-    internal record struct JActionTask
+    internal struct JActionTask
     {
         /// <summary>The type of task operation.</summary>
         internal JActionTaskType Type;

UnityProject/Packages/com.jasonxudeveloper.jengine.util/Runtime/JActionAwaitable.cs

@@ -21,8 +21,18 @@ namespace JEngine.Util
     /// for proper compiler warnings when not awaited.
     /// </para>
     /// </remarks>
-    public readonly record struct JActionAwaitable(JAction Action)
+    public readonly struct JActionAwaitable
     {
+        /// <summary>The JAction instance being awaited.</summary>
+        public readonly JAction Action;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="JActionAwaitable"/> struct.
+        /// </summary>
+        /// <param name="action">The JAction to await.</param>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public JActionAwaitable(JAction action) => Action = action;
+
         /// <summary>
         /// Gets the awaiter for this awaitable.
         /// </summary>
@@ -39,8 +49,18 @@ public readonly record struct JActionAwaitable(JAction Action)
     /// This struct implements <see cref="ICriticalNotifyCompletion"/> to support
     /// both regular and unsafe continuations, enabling efficient async state machine behavior.
     /// </remarks>
-    public readonly record struct JActionAwaiter(JAction Action) : ICriticalNotifyCompletion
+    public readonly struct JActionAwaiter : ICriticalNotifyCompletion
     {
+        /// <summary>The JAction instance being awaited.</summary>
+        public readonly JAction Action;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="JActionAwaiter"/> struct.
+        /// </summary>
+        /// <param name="action">The JAction to await.</param>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public JActionAwaiter(JAction action) => Action = action;
+
         /// <summary>
         /// Gets whether the <see cref="JAction"/> has completed execution.
         /// </summary>