Switch from the deprecated `interp2d` to `RectBivariateSpline `
The purpose of this MR is to switch from the deprecated interp2d to RectBivariateSpline. As part of this MR we have introduced a modified version of scipy.interpolate.RectBivariateSpline to add kwargs that were previously available in interp2d. This is related to !793 (merged) and reverts !796 (merged).
Edited by Charlie Hoy