Not blocking the creation and addition of pulses with zero duration

[HGSilveri]

When doing a sweep over the duration of a pulse, users often want to start with a duration of 0. This is currently blocked at the moment the waveform is created (and meaningfully so, as it is undefined in many cases what exactly a waveform with zero duration is).

Ideally, we would not allow the creation of waveforms with zero duration under normal circumstances, but could potentially allow it in the creation of a parametrized sequence. Then, when it were to be added to the sequence, it would raise an warning saying that a pulse of 0 duration doesn't mean anything and just skip it.

I have many reserves about this, as in the end it ends up resulting in a lot of changes and exceptional cases just for convenience in one particular scenario. Nonetheless, I see the value in it, so I think it's worth considering.