chore: initialize standalone UPM package

CodeGen/Editor/Unity.ShrinkNetwork.EventBus.CodeGen.asmdef

@@ -0,0 +1,19 @@
+{
+  "name": "Unity.ShrinkNetwork.EventBus.CodeGen",
+  "rootNamespace": "ShrinkNetwork.Integration.CodeGen",
+  "references": [
+    "ShrinkNetwork.Integration.EventBus",
+    "Unity.ShrinkEventBus.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
+}