Bukkit Async Scheduler (every refresh_seconds)
            ↓
  build() → snapshotBalances() for each currencyId
            sorted DESC by balance
            Bukkit.getOfflinePlayer(uuid) to resolve names
            ↓
  CachedTop { List<TopEntry>, rankByUuid: Map<UUID,Integer> }
            ↓
  ConcurrentHashMap caches.put(currencyId, cached)

top:
  refresh_seconds: 300        # recalculate every 5 min (300 s)
  change_threshold: 0       # invalidate cache only if |Δ| > threshold

TopCacheService.invalidateAll()         → clears all currencies
TopCacheService.invalidate(currencyId)  → clears one specific currency

class TopEntry {
  int     rank;      // 1-based
  UUID    uuid;
  String  name;      // OfflinePlayer.getName() or UUID[:8]
  double  balance;   // raw unformatted value
}