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

[S1M0N38]

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