Sign of pulse parameters is not deserialized properly

[stavros11]

pulse = Pulse(0, 40, 0.3, int(4e9), 0.0, shape="Drag(5, -0.02)")
print(pulse)

gives

Pulse(0, 40, 0.3, 4_000_000_000, 0, Drag(5, 0.02), None, PulseType.DRIVE, 0)

so -0.02 is converted to 0.02. I am not sure if this has any practical consequence in this case.

I found this while working on #789 for 0.2, but then I realized that it also exists for 0.1. I am guessing it will be solved by #818 where the ugly eval will be dropped, so I would even postpone for 0.2. @alecandido if you agree, we can put this directly to the 0.2 milestone.

[alecandido]

I agreed and added to the milestone.

And indeed, by avoiding parsing the strings manually, these errors should become almost impossible.