Make more use of refinement.

The Expression base class could implement fallback binary operators such as the following:

@convert_operands(sameShape = True)
@refine_operands
def __add__(self, other):
    return NotImplemented

This would allow any expression that does not have __add__ but refines to another expression that has __add__ to be summed with a numeric constant. For instance, you could then write geomean(c) + 5 if c is constant.¹

¹Right now this gives TypeError: unsupported operand type(s) for +: 'GeometricMean' and 'int' as GeometricMean does not define __add__ at all while int has no clue that it would need to refine its partner and convert itself.