Add missing Babel plugins for build-library

- Add @babel/plugin-proposal-object-rest-spread
- Add @babel/plugin-syntax-dynamic-import
- These were missing dependencies revealed by pnpm's stricter isolation
- Fixes build-library errors in CI

Author: captbaritone

packages/webamp/package.json

@@ -74,7 +74,9 @@
   "devDependencies": {
     "@babel/plugin-proposal-class-properties": "^7.18.6",
     "@babel/plugin-proposal-nullish-coalescing-operator": "^7.18.6",
+    "@babel/plugin-proposal-object-rest-spread": "^7.20.7",
     "@babel/plugin-proposal-optional-chaining": "^7.21.0",
+    "@babel/plugin-syntax-dynamic-import": "^7.8.3",
     "@babel/preset-env": "^7.25.0",
     "@parcel/reporter-bundle-analyzer": "^2.8.2",
     "@rollup/plugin-babel": "^6.0.4",