refactor: adjust internal vnode types + more dts tests

test-dts/util.ts

@@ -0,0 +1,4 @@
+// aesthetic utility for making test-d.ts look more like actual tests
+// and makes it easier to navigate test cases with folding
+// it's a noop since test-d.ts files are not actually run.
+export function describe(_name: string, _fn: () => void) {}