Cyrk flat DiffEq fix

[dihm]

Fixes error with eqns='flat' option for cyrk_solve with stacks of EoM.

[dihm]

Upon further testing, this is not a complete fix. It turns out that Sensor.get_time_hamiltonian_components returns different stack shapes depending on whether the scanned component is a time-dependent Rabi frequency or not, and those situations require different handling within the flat DiffEq. Going to have to go back to the drawing board a little bit to figure out how to best handle this situation.