feat: make Unity integration optional

CodeGen/Editor/Unity.ShrinkEventBus.CodeGen.asmdef

@@ -1,24 +1,29 @@
 {
-    "name": "Unity.ShrinkEventBus.CodeGen",
-    "rootNamespace": "ShrinkEventBus.CodeGen",
-    "references": [
-        "ShrinkEventBus.Runtime",
-        "Unity.ShrinkShared.CodeGen"
-    ],
-    "includePlatforms": [
-        "Editor"
-    ],
-    "excludePlatforms": [],
-    "allowUnsafeCode": true,
-    "overrideReferences": true,
-    "precompiledReferences": [
-        "Mono.Cecil.dll",
-        "Mono.Cecil.Mdb.dll",
-        "Mono.Cecil.Pdb.dll",
-        "Mono.Cecil.Rocks.dll"
-    ],
-    "autoReferenced": false,
-    "defineConstraints": [],
-    "versionDefines": [],
-    "noEngineReferences": false
+  "name": "Unity.ShrinkEventBus.CodeGen",
+  "rootNamespace": "ShrinkEventBus.CodeGen",
+  "references": [
+    "ShrinkEventBus.Runtime"
+  ],
+  "includePlatforms": [
+    "Editor"
+  ],
+  "excludePlatforms": [],
+  "allowUnsafeCode": true,
+  "overrideReferences": true,
+  "precompiledReferences": [
+    "Mono.Cecil.dll",
+    "Mono.Cecil.Mdb.dll",
+    "Mono.Cecil.Pdb.dll",
+    "Mono.Cecil.Rocks.dll"
+  ],
+  "autoReferenced": false,
+  "defineConstraints": [],
+  "versionDefines": [
+    {
+      "name": "com.cneicy.shrink-shared-codegen",
+      "expression": "0.2.1",
+      "define": "SHRINK_EVENTBUS_HAS_SHARED_CODEGEN"
+    }
+  ],
+  "noEngineReferences": false
 }