>Worth pointing out both here and in applyShear that the argument cannot be a function of wavelength ...

Yup.  Added the following to applicable `apply*` methods.
```
        Note that, in contrast to applyDilation, applyExpansion, and applyShift, this method cannot
        accept a function of wavelength as its argument.  If you find a use case for this, however,
        please submit an issue to https://github.com/GalSim-developers/GalSim/issues
```