Export server/router (#84)

- Export `createRouter` by exporting the HTTP handler so we can use
`fetch` function from it inside tests without starting a real server
- Export `close` method in the return value of `serve` so we can use
start and stop server
- Avoid top-level await for better support in most envs
- In case of `npm install` from another project, it runs `tsc` to
generate js and declaration files to be used in our Hive GW test suite
here;
graphql-hive/gateway#120

---------

Co-authored-by: Kamil Kisiela <kamil.kisiela@gmail.com>

package.json

@@ -48,14 +48,15 @@
     "summary": "tsx ./src/summary.ts",
     "build": "tsc",
     "typecheck": "tsc --noEmit",
-    "format": "prettier --write ."
+    "format": "prettier --write .",
+    "postinstall": "npx tsc --project tsconfig.json --noCheck --noResolve"
   },
   "dependencies": {
     "@apollo/composition": "2.9.3",
     "@apollo/subgraph": "2.9.3",
     "async-retry": "1.3.3",
     "dotenv": "16.4.5",
-    "fets": "0.8.3",
+    "fets": "0.8.4",
     "get-port": "7.1.0",
     "graphql": "16.9.0",
     "graphql-yoga": "5.10.2",
@@ -77,7 +78,7 @@
     "express": "5.0.1",
     "prettier": "3.3.3",
     "tsx": "4.19.2",
-    "typescript": "5.6.3",
-    "wgc": "0.70.1"
+    "wgc": "0.70.1",
+    "typescript": "5.6.3"
   }
-}
+}