[jss-expand] Observables not respected properly

Using TC39-compliant observables from Knockout:

```js
const observable = ko.observable('normal')
animation: {
name: 'anim',
duration: '0.25s',
direction: observable,
}
```

One would expect the result to be `anim 0.25s 123` but instead it's `anim 0.25s [Object object]`.

The issue names the jss-expand subsystem but provides no file or test path. Reproduce the Knockout observable example and inspect how jss-expand processes the animation direction value. Done means the observable is respected and the generated result uses the expected direction value instead of [Object object].

Written by the indexing model from the issue text.