Turn Waveform into a bare array

[alecandido]

Now Waveform is only useful as a type hint.

There is only one caveat: Waveform was hashable, np.ndarray is not (because mutable). The gap was filled by calling array.tobytes() (since the generated bytes are immutable, as a snapshot of an array at a specific time).
It's not optimal, since it's still a hash of an actually mutable object, but we just have to be consistent.

However, I'm still using the trick explicitly in QM.
Are you aware of any other place where the Waveform had to be hashable?

[codecov]

Codecov Report

Attention: 7 lines in your changes are missing coverage. Please review.

Comparison is base (a5b7248) 61.94% compared to head (ba476ee) 61.68%.

Files	Patch %	Lines
src/qibolab/pulses/shape.py	82.60%	4 Missing ⚠️
src/qibolab/instruments/qblox/sequencer.py	0.00%	3 Missing ⚠️

Additional details and impacted files

@@                 Coverage Diff                  @@
##           simplify-pulse-7     #774      +/-   ##
====================================================
- Coverage             61.94%   61.68%   -0.26%     
====================================================
  Files                    52       51       -1     
  Lines                  5723     5690      -33     
====================================================
- Hits                   3545     3510      -35     
- Misses                 2178     2180       +2     

Flag	Coverage Δ
unittests	61.68% <82.05%> (-0.26%)	⬇️

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[stavros11]

I did not test (further than CI), but looks good to me. I think we can postpone hardware testing to 0.2 branch after all these are merged because now it's already pointing to other branches.

However, I'm still using the trick explicitly in QM. Are you aware of any other place where the Waveform had to be hashable?

Personally, I am not aware. For QM, we need to associate a name (str) to each waveform in order to register it in the config and assign it to pulses. In principle str(id(waveform)) would even work, but hash is better because it is the same for equal waveforms, so we don't need to register the same waveform multiple times (eg. during unrolling), while id is different for every instance (if I am correct). But I believe your current solution is okay (alternatives https://stackoverflow.com/questions/16589791/most-efficient-property-to-hash-for-numpy-array)