[FEAT]: Add Coins and gems to player model

[coxmars]

Issue

Modify Player Model to Add Coins and Stones Fields

Description

We need to modify the existing Player model to include coins and stones fields that will represent the player's in-game virtual currencies. These fields will track the player's balance of both currency types and integrate with the credit system and marketplace functionality.

Explanation

The Player model currently lacks fields for tracking virtual currencies (coins and stones) that are essential for the game's economy. This modification will add the necessary fields and related functionality to manage player currency balances.

Technical Spike Goals:

• Add coins and stones fields to the Player struct/model
• Implement getter and setter methods for currency management
• Create currency validation and balance checking logic
• Update player initialization to set default currency values
• Modify existing player-related functions to handle currency fields
• Update all player-related tests to include currency field testing