Adaptive time-stepping for transient solver using SUNDIALS

[simlapointe]

Add adaptive time-stepping capability for transient simulations. The default transient solver type remains a fixed time-stepping integrator, but the user can now use SUNDIALS implicit multistep (CVODE) and Runge-Kutta (ARKODE) integrators if desired.

[hughcars]

Looking good. There's a few smaller structural issues, but the two bigger things I am thinking about
a) Can the RUNGE_KUTTA option use instead the mfem internal time integrator? That way the sundials connection is really only used for the adaptivity. This would slightly tidy the interface for adaptivity, along with making the non-adaptive slightly more fully featured. There are some SDIRK options in there that would probably be good choices.
b) Is there a way to compute B implicit to this process?

I have some of my suggestions on hughcars/transient-adapt-dt if you want to take a look.

[simlapointe]

I updated the config file defaults and parameter checking so we can use appropriate constraints in the json script. Using some existence checks and a few if's in config.cpp to remove the need for the exhaustive if/else's I had in iodata.cpp.

[hughcars]

Looking good, some small things I missed on the previous pass and thinking a little about if there's more we can delete. Additionally, need to rebase on top of main.

[hughcars]

Looks good to me! Merge away 🚀