Model correction of flux(lambda) for differential atmospheric diffraction

For IFU data this is instead a WCS pointing correction as a function of wavelength.

The issue only identifies IFU data and a WCS pointing correction as a function of wavelength; no file, test, or entry point is named. Start by locating the code handling wavelength-dependent WCS corrections and determine the expected behavior for IFU observations. Done means the correction is implemented and verified for the relevant data.

Written by the indexing model from the issue text.