Refactor tests to use both solvers for all analytical tests

[K20shores]

Refactor test cases so that either Rosenbrock or Backward Euler can be used.

Blocked by #500

Acceptance Criteria

• All analytical ODE solver tests are applied to the Backward Euler solver, and they all pass

Ideas

• Create an analytical_backward_euler.cpp test following the logic of https://github.com/NCAR/micm/blob/main/test/integration/analytical_rosenbrock.cpp