[FEAT]: Add food improvement for purchases

[coxmars]

Issue

Adapt Food Model to Allow Purchases with Virtual Currencies

Description

We need to modify the food model to support purchases using virtual currencies (coins and stones) instead of or in addition to other payment methods. This will integrate the food system with the game's virtual economy and allow players to buy food using their in-game currency balances.

Explanation

The current food model likely doesn't support virtual currency transactions. This adaptation will enable players to purchase food items using their coins and stones, creating a complete in-game economy loop.

Technical Spike Goals:

• Add virtual currency pricing fields to food model (coins_price)
• Implement purchase validation methods to check player currency balances
• Create currency deduction logic for successful food purchases
• Add support for different payment methods (coins)
• Create comprehensive tests for virtual currency food purchase scenarios

Notes

• In Golem Runner we did it with an unlock field in the model, you can do it like that or figure out by yourself: https://github.com/AkatsukiLabs/GolemRunner/blob/76b5c5e8adf8b182dfc3c7f3156ad39b52155810/contract/src/models/golem.cairo#L22