Test implicit stepper convergence conditions

[juliasloan25]

Is your feature request related to a problem? Please describe. Currently, we initialize our IMEX algorithm with max_iters = 1. While using fewer iterations is better for performance, it also increases the likelihood of larger errors in both our solution values and mass conservation. We need to test different convergence conditions with larger max_iters to find a tolerance that produces reasonable RMSE and mass conservation error.

We should produce a plot comparing convergence conditions with RMSE and mass conservation error.

Additional context

• Celia 1990
  • Compare convergence conditions, error