text: Title: imageio: fps no longer supported, use duration instead
  Body: https://github.com/polakowo/vectorbt/blob/8c040429ac65d43ea431dc2789bf4787dd103533/vectorbt/utils/image_.py#LL74C1-L74C72
  
  Clearly `vbt.save_animation` is still using `fps` as argument in `imageio.get_writer`, which doesn't support `fps` anymore,
  One quick fix should be changing this line to
  
  `with imageio.get_writer(fname, duration=fps // 5, **writer_kwargs) as writer:`