test(astro): add tests (#5069)

This adds about 85% coverage. It is not perfect. I looked a bit into Astro testing and it gets a bit complex.
But, it gets us pretty far.
And this shows the problems I saw in GH-5052.
After this lands, I can verify that GH-5052 improves things.

Closes GH-5060.

Author: wooorm-arcjet

arcjet-astro/package.json

@@ -47,7 +47,9 @@
     "build": "rollup --config rollup.config.js",
     "lint": "eslint .",
     "prepublishOnly": "npm run build",
-    "test": "npm run build && npm run lint"
+    "test-api": "node --test",
+    "test-coverage": "node --experimental-test-coverage --test",
+    "test": "npm run build && npm run lint && npm run test-coverage"
   },
   "dependencies": {
     "@arcjet/env": "1.0.0-beta.11",