Bug in area operator `Az` and potentially other operators...

Hi, I am trying to do a simple computation of the surface area of a grid. When I use the existing Oceananigans Operators, I get a very strange surface area. For example: ```Julia using Oceananigans using Oceananigans.Operators: Az Nz = 32 grid = RectilinearGrid(size=(32, 32, Nz), extent=(1, 1, 1)) field_test = Field{Center, Center, Nothing}(grid) set!(field_test, 1) area = field_test * Az tot_area = Integral(area, dims=(1, 2)) |> Field @show tot_area[1, 1, 1] ``` Gives `tot_area[1, 1, 1]= 0.0009765625` -- when we would expect `1`! Any ideas what is going on here? cc @navidcy who I was debugging this with.