Resolve "Deprecated: ndarray of different length lists (SamplingCounterAcquisitionSlave)"

Closes #1958 (closed)

The MR preserves the previous behaviour, only explicit to not have the warning

>>> import numpy
>>> type(numpy.array([[1,2], [1,2,3]])[0])
__main__:1: VisibleDeprecationWarning: Creating an ndarray from ragged nested sequences (which is a list-or-tuple of lists-or-tuples-or ndarrays with different lengths or shapes) is deprecated. If you meant to do this, you must specify 'dtype=object' when creating the ndarray
<class 'list'>
>>> type(numpy.array([[1,2], [1,2,3]], dtype=object)[0])
<class 'list'>