Account for accelerations in reaction forces

The reaction force calculation in the solid mechanics module assumes that the accelerations are zero:

https://github.com/LLNL/serac/blob/ef413804eda27556cec2b456ac45b44c830b23c1/src/serac/physics/solid_mechanics.hpp#L669-L673

This is fine for quasi-statics, but for dynamics, we must pass the updated accelerations in the second slot. It's not clear how to get this quantity out of the ODE solvers at the moment.

Start at src/serac/physics/solid_mechanics.hpp:669-673 and trace how the reaction force calculation receives its acceleration arguments. Then inspect the ODE solver interfaces to determine how updated accelerations can be obtained and passed in the second slot; done means dynamic reaction forces account for nonzero accelerations without changing quasi-static behavior.

Written by the indexing model from the issue text.