Make sure that time_steps (and all other parameters) are handled consistently between the simulation functions

[baurse]

The meaning of the "time_steps" parameter is slightly different for the RK4-based simulation functions compared to the ETDRK4 based KS simulation: For the former, time_steps=1 only returns the initial condition, while time_steps=1 returns the first simulation step for the KS simulation!

This is an unnecessary stumbling block and should be standardized, probably to the former's behavior.
Intuition: time_steps = length of output, including the initial condition.