feat: add cross-engine runtime support

Runtime/ShrinkContextDefaults.cs

@@ -1,5 +1,7 @@
 #nullable enable
+#if UNITY_5_3_OR_NEWER
 using UnityEngine;
+#endif
 
 namespace ShrinkContext
 {
@@ -13,7 +15,9 @@ namespace ShrinkContext
 
         public static ShrinkContextRuntime Default => _default ??= new ShrinkContextRuntime();
 
+#if UNITY_5_3_OR_NEWER
         [RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.SubsystemRegistration)]
+#endif
         private static void ResetStaticState()
         {
             _default = null;

package.json

@@ -1,6 +1,6 @@
 {
   "name": "com.cneicy.shrink-context-core",
-  "version": "0.1.0",
+  "version": "0.2.0",
   "displayName": "ShrinkContext Core",
   "description": "Cordis 时空可组合性范式的 Unity/C# 原型核心：可逆效应追踪、响应式余效应与组件纤程生命周期。",
   "unity": "2022.3",