CyRK's CySolver does not allow for complex-valued dependent variables.

CyRK's CySolver only allows `np.float64` y0 and dydt. This is due to limitations between fused types (used in `cyrk_ode`) and cython cdef classes.

A workaround is to convert your N-dimensional complex system of ODEs into a 2N-dimensional floating point system of ODEs. Pass this onto CySolver, and then convert the output back into complex values. 