chore: migrate to @typescript/native-preview (tsgo)

packages/test-utils/package.json

@@ -7,7 +7,7 @@
   "type": "module",
   "scripts": {
     "build": "node ../../scripts/build_package.js",
-    "typecheck": "tsc --noEmit"
+    "typecheck": "tsgo --noEmit"
   },
   "dependencies": {
     "@google/gemini-cli-core": "file:../core",
@@ -16,10 +16,10 @@
     "strip-ansi": "^7.1.2",
     "vitest": "^3.2.4"
   },
-  "devDependencies": {
-    "typescript": "^5.3.3"
-  },
   "engines": {
     "node": ">=20"
+  },
+  "devDependencies": {
+    "@typescript/native-preview": "^7.0.0-dev.20260412.1"
   }
 }