ci: add verify-types job to prevent missing typings on publish (#1576)

## Summary

Preventive measures to avoid a repeat of #1573.

### CI: new `verify-types` job

Adds a dedicated CI job that runs `npm run build:types` in parallel with
unit tests on every PR. If type declaration generation fails, the build
fails before merge.

### Remove `scripts/prepack.js`

This file originally existed to flatten rpt2's output — rpt2 dumped
declarations into `dist/typings/src/` instead of `dist/typings/`, so the
script moved them up before publish.

Since #1574 moved declaration generation to `tsc --project
tsconfig.types.json`, this script became dead code. `tsc` outputs
directly to `dist/typings/` with no `src/` subdirectory. More
importantly, if `tsc` fails it exits non-zero — stopping the `prepack`
chain and blocking publish. A separate guard file adds nothing on top of
that.

`prepack` simplified from:
```
npm run build && npm run build:types && node ./scripts/prepack
```
to:
```
npm run build && npm run build:types
```

Author: yogeshchoudhary147

.github/workflows/test.yml

@@ -78,6 +78,32 @@ jobs:
         uses: codecov/codecov-action@57e3a136b779b570ffcdbf80b3bdc90e7fab3de2 # pin@6.0.0
         with:
           token: ${{ secrets.CODECOV_TOKEN }}
+
+  verify-types:
+    needs: test
+
+    name: Verify Type Declarations
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v6
+
+      - name: Setup Node
+        uses: actions/setup-node@v6
+        with:
+          node-version: ${{ env.NODE_VERSION }}
+          package-manager-cache: false
+
+      - name: Restore build artifacts
+        uses: actions/cache/restore@v5
+        with:
+          path: .
+          key: ${{ env.CACHE_KEY }}
+
+      - name: Generate type declarations
+        run: npm run build:types
+
   gatsby:
     needs: test
 

package.json

@@ -51,7 +51,7 @@
     "serve:coverage": "serve coverage/lcov-report -n",
     "serve:stats": "serve bundle-stats -n",
     "print-bundle-size": "node ./scripts/print-bundle-size.mjs",
-    "prepack": "npm run build && npm run build:types && node ./scripts/prepack",
+    "prepack": "npm run build && npm run build:types",
     "publish:cdn": "ccu --trace"
   },
   "devDependencies": {