SPIKE: convert integration tests to gts/gjs

showcase/package.json

@@ -63,6 +63,7 @@
     "@tsconfig/ember": "^3.0.10",
     "@types/qunit": "^2.19.12",
     "@types/rsvp": "^4.0.9",
+    "@types/sinon": "^17.0.4",
     "broccoli-asset-rev": "^3.0.0",
     "concurrently": "^9.1.2",
     "ember-a11y-testing": "^7.1.2",
@@ -131,5 +132,9 @@
   },
   "ember": {
     "edition": "octane"
+  },
+  "exports": {
+    "./tests/*": "./tests/*",
+    "./*": "./app/*"
   }
 }