fix: show unequipped arrow packs in the bag without relogging

- Equipment.UnequipItem sends MsgItemInfo AddItem for arrow packs and keeps Update for all other gear

- The 6609 unequip handler leaves arrow packs out of its bag and waits for the server to add them, so the Update-only publish left them hidden until relog

- Add a regression test for the arrow unequip packet and document the arrow exception in the hidden attribute notes