Trapz dx doesn't trigger array_function mechanism

[mocquin]

This is numpy-related issue : given the current interface, we can't do anything about this problem.
An issue is opened at numpy with a dummy example : numpy#18902

In the case of physipy :

from physipy import m
import numpy as np

arr = np.arange(10)
q = arr * m

# all these work
print(np.trapz(arr, arr, dx=0.5))
print(np.trapz(arr, q, dx=0.5))
print(np.trapz(arr, arr, dx=0.5*m))
print(np.trapz(arr, dx=0.5))
print(np.trapz(q, dx=0.5*m))

# but not this one 
print(np.trapz(arr, dx=0.5*m))