Update ozark conservation test for IMEX stepping

[juliasloan25]

Is your feature request related to a problem? Please describe.
In #651, we convert the SoilCanopy model from being entirely explicitly-stepped to using explicit and implicit timestepping for different variables. This invalidates the conservation calculations we were previously using (see this link for more details).

We should re-think this test and update the calculations to accurately check conservation if possible.