Update counts to handle floats/NaN values from hardware

[lillian542]

The QuEra hardware sometimes has failed measurements, which return as NaN. Because of this, all samples from the device are returned with type float, and some of them are np.NaN. These were not handled well in counts. On the _default_qubit device, nothing was converted to integers, so it did this:

{'0.00.00.0': 149,
'0.00.01.0': 281, 
'0.00.0nan': 2,
'0.01.00.0': 277,
'0.01.01.0': 4,
'0.0nan0.0': 4,
'1.00.00.0': 268,
'1.00.0nan': 2,
'1.01.00.0': 5,
'nan0.00.0': 8}

We don't like that. Now they are converted into integers if there is no observable, just like in CountsMP.

Also added a line both there and in CountsMP to avoid converting the NaN values to 0 and implying they were ground state measurements - instead, any sample where at least one wire failed is disregarded when totalling the number of counts.

Has been tested with the QuEra hardware, and now returns nicely:

>>> res = circuit(params)
>>> res
{'000': 230, '001': 251, '010': 252, '011': 1, '100': 249, '110': 4}

with 13 disregarded failed measurements:

>>> sum(count for count in res.values())
987

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[lillian542]

[sc-48588]

[albi3ro]

changelog?

Thanks for this fix 🎉