SciPy deprecation warning for scipy.integrate.cumtrapz

[vsnever]

When calculating with the Beam, SciPy 1.12 raises DeprecationWarning:

DeprecationWarning: 'scipy.integrate.cumtrapz' is deprecated in favour of 'scipy.integrate.cumulative_trapezoid' and will be removed in SciPy 1.14.0

Therefore, we need to replace deprecated cumtrapz() with the cumulative_trapezoid() in SingeRayAttenuator._beam_attenuation(). However, the new name was only introduced in SciPy 1.7, and the tests fail in the Python 3.7 + oldest-supported-numpy environment.

I suggest using:

try:
    from scipy.integrate import cumulative_trapezoid
except ImportError:
    from scipy.integrate import cumtrapz as cumulative_trapezoid

[vsnever]

Fixed in #437.