Additional typegen asserts (#2448)

* Additional typegen asserts

* typo

* Revert tuple assert

* Free-standing Vec is valid

packages/typegen/package.json

@@ -40,7 +40,7 @@
     "@polkadot/metadata": "1.26.0-beta.1",
     "@polkadot/rpc-provider": "1.26.0-beta.1",
     "@polkadot/types": "1.26.0-beta.1",
-    "@polkadot/util": "^2.18.1",
+    "@polkadot/util": "^3.0.0-beta.3",
     "handlebars": "^4.7.6",
     "websocket": "^1.0.31",
     "yargs": "^15.4.1"