Unlock and track player achievements via the Epic Online Services Achievements interface

Steps

1. Initialize the EOS Achievements interface with a valid platform handle obtained after SDK initialization
2. Call QueryDefinitions to fetch the achievement definitions for the product, which provides the list of achievement IDs and unlock criteria
3. Call QueryPlayerAchievements with the local user handle to retrieve the current unlock state and progress for all achievements for that player
4. Update player stat values via the EOS Stats interface (IngestStat) which drives stat-based achievement unlock logic on the backend
5. Register a notification callback via AddNotifyAchievementsUnlocked to receive real-time events when the server evaluates stats and unlocks an achievement
6. On the unlock notification, surface the achievement to the player in-game and call QueryPlayerAchievements again to refresh the local achievement state