Handle props access on base object

[ssalbdivad]

Currently this crashes:

import { generic, Hkt } from "arktype";

const Enum = generic(["O", "object"])(
  ({ O }) => {
    console.log(O.props); // TypeError: this.applyStructuralOperation[0] is not iterable
  },
  class extends Hkt {
    declare body: this[0];
  }
);

This is based on props only existing on nodes with an actual structure, but we need to find a better way to work around that for object.