📝 **Task:** Implement `FlagSet.is_enabled(flag, user_id)`. Rules are dicts with optional `overrides: {user_id: bool}` and `rollout_pct: int` (0-100). Override wins over rollout. Unknown flag returns False. Bucket = `int(md5(f"{flag}:{user_id}").hexdigest(), 16) % 100`; enabled when `bucket < rollout_pct`. 📋 Implement the function above. Tests run automatically. 💡 **Hint:** Re-read the theory if stuck.