fix!(gamestate): used_vouchers keys has empy values.

We are expecting

```
"used_vouchers": {
"v_petroglyph": "effect of the voucher ...",
"v_wasteful": "effect of the voucher ...",
...
},
```

but instead we are getting

```
"used_vouchers": {
"v_petroglyph": "",
"v_wasteful": "",
...
},
```

This is consider a BREAKING CHANGE because would impact the information that is parsed in BalatroLLM strategy so it would be an unfair advantage for the new runs in balatrobench.com