EngUnit doesn't handle __init__ from other EngUnits properly

[SMMB-DEV]

Suppose I want to divide a voltage by a resistance and give it the unit A.

V = EngUnit(5, unit='V')
R = EngUnit(1.2, unit='Ω')
I = V / R
I.unit = 'A'

If I instead do this:

I = EngUnit(V / R, unit='A')

when I try to print I, I get an exception saying "'EngNumber' object has no attribute 'number'".

EngUnit has an eng_num member of type EngNumber. If the value passed to EngUnit.__init__() isn't a string, it tries to create an EngNumber direcly from value. Inside EngNumber.__init__(), value has to be one of str, int, float, EngNumber or numpy.integer and since the value here is none of those (EngUnit), it doesn't create the number member of EngNumber.