Saving and loading pulse objects

[jack-champagne]

Now that typed pulse objects (SplinePulse, ZeroOrderHoldPulse, LinearPulse) exist
and are an important work product, add serialization support (save/load) so pulses can
be persisted and resampled across sessions (likely via JLD2).

[l997RaghavAnand]

this looks like an interesting issue how do you see the approach on this