feat: make Unity integration optional

Integration/Tests/SharedDispatcherTests.cs

@@ -0,0 +1,43 @@
+#if SHRINK_EVENTBUS_HAS_SHARED_RUNTIME
+using System;
+using NUnit.Framework;
+using ShrinkSDK.Runtime;
+
+namespace ShrinkEventBus.Integration.Tests
+{
+    public sealed class SharedDispatcherTests
+    {
+        private sealed class Dispatcher : IShrinkMainThreadDispatcher
+        {
+            public bool IsMainThread => false;
+            public Action Pending;
+            public bool TryPost(Action action) { Pending = action; return true; }
+        }
+
+        [Test]
+        public void AdapterPreservesAffinityAndPostsThroughSharedDispatcher()
+        {
+            var original = ShrinkEventBusRuntime.MainThreadDispatcher;
+            try
+            {
+                var dispatcher = new Dispatcher();
+                var adapter = new ShrinkSharedMainThreadDispatcher(dispatcher);
+                ShrinkEventBusRuntime.ConfigureMainThreadDispatcher(adapter);
+                Assert.IsFalse(ShrinkEventBusRuntime.MainThreadDispatcher.IsMainThread);
+                var hits = 0;
+                Assert.IsTrue(ShrinkEventBusRuntime.MainThreadDispatcher.TryPost(() => hits++));
+                Assert.AreEqual(0, hits);
+                dispatcher.Pending();
+                Assert.AreEqual(1, hits);
+            }
+            finally { ShrinkEventBusRuntime.ConfigureMainThreadDispatcher(original); }
+        }
+
+        [Test]
+        public void AdapterRejectsNullDispatcher()
+        {
+            Assert.Throws<ArgumentNullException>(() => new ShrinkSharedMainThreadDispatcher(null));
+        }
+    }
+}
+#endif