Further test inverse relationship between CAM_var_conversion and SAM_var_conversion

[dorchard]

Current tests in test_cam_interface.f90 test whether SAM_var_conversion is the left inverse of CAM_var_conversion, i.e., if f = CAM_var_conversion : CAM -> SAM and g = SAM_var_conversion : SAM -> CAM then we have tests that g . f = id, e.g.:

• https://github.com/m2lines/convection-parameterization-in-CAM/blob/main/tests/test_CAM_interface/test_cam_interface.F90#L323-L324
• https://github.com/m2lines/convection-parameterization-in-CAM/blob/main/tests/test_CAM_interface/test_cam_interface.F90#L388-L389

There is then an opportunity to test whether CAM_var_conversion is also the weak left inverse of SAM_var_conversion by checking f . g . f = f (this is sometimes called a 'semigroup inverse').

All we would need to do is save the outputs from the version conversion f and compare those with the results after an extra CAM_var_conversion.