feat: improve background and character loading

[Kirpal]

Description

I added a class to improve the loading of assets, by loading them when the app first starts. It also prioritizes loading the initially selected character and background, before loading the rest of the assets.

Type of Change

• ✨ New feature (non-breaking change which adds functionality)
• 🛠️ Bug fix (non-breaking change which fixes an issue)
• ❌ Breaking change (fix or feature that would cause existing functionality to change)
• 🧹 Code refactor
• ✅ Build configuration change
• 📝 Documentation
• 🗑️ Chore

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