Clarify and enforce which integrators are valid for each problem type: - Private Piccolissimo integrators should work with `SplinePulseProblem` - `SmoothPulseProblem` and `BangBangProblem` should only accept zero-order hold pulses
Clarify and enforce which integrators are valid for each problem type:
SplinePulseProblemSmoothPulseProblemandBangBangProblemshould only accept zero-order hold pulses