Extra functions to work with MapSets.
Removes the item if present, adds if missing
@spec toggle(MapSet.t(), any()) :: MapSet.t()
iex> Box.MapSet.toggle(MapSet.new([1, 2]), 1) MapSet.new([2])
iex> Box.MapSet.toggle(MapSet.new([1, 2]), 3) MapSet.new([1, 2, 3])