Vertical regrid should not extrapolate data

# 🐜 Bug Report
Linear vertical regridding from a grid with an 80km top of atmosphere to an 85km top of atmosphere results in extrapolated values in the top 5km. In the case of ozone concentration, this includes unphysical negative numbers.

To be consistent with horizontal regridding in both regular ANTS and UG-ANTS, we should use NaN values instead of extrapolating in the general regrid application. If a particular science code needs a different extrapolation, it can call the regrid library code with that extrapolation option.

Start by locating the general regrid application and compare its vertical behavior with horizontal regridding in regular ANTS and UG-ANTS. Read the regrid library's extrapolation options before changing the application behavior. Done means the top 5km uses NaN rather than extrapolated values, while science-specific callers can still request another extrapolation option.

Written by the indexing model from the issue text.