[FEAT]: Create methods/logic to add/decrease coins and gems in player's balance

[coxmars]

Issue

Create Methods in Player Model to Add and Spend Coins and Stones

Description

We need to implement methods in the Player model to handle adding and spending both virtual currencies (coins and stones). These methods will provide the core functionality for managing player currency balances throughout the game economy.

Explanation

The Player model requires dedicated methods for currency management operations. These methods will ensure proper validation, balance checking, and secure transaction handling for both coins and stones currencies.

Technical Spike Goals:

• Create add_coins and spend_coins methods with balance validation
• Create add_stones and spend_stones methods with balance validation
• Implement insufficient balance error handling and validation
• Add transaction logging/history for currency operations
• Create comprehensive tests for all currency addition and spending scenarios