Add option to return dataset on cmod_functions format

[Sosnowsky]

grid_r, grid_z = np.meshgrid(ds.x.values, ds.y.values)
ds = xr.Dataset(
        {"frames": (["y", "x", "time"], ds.n.values)},
        coords={
            "R": (["y", "x"], grid_r),
            "Z": (["y", "x"], grid_z),
            "time": (["time"], ds.t.values),
        },
    )
return ds