Function semi_implicit_step 

pub fn semi_implicit_step<T: NabledReal + Default + LuProviderScalar>(
    ctx: &RobotContext<T>,
    state: &SimState<T>,
    tau: &ArrayView1<'_, T>,
    config: &SimConfig<T>,
) -> Result<SimStepResult<T>, SimError>

Advance (q, qd) by one semi-implicit Euler step using forward dynamics.