I'm Italian too and I AM from Cassano Magnago!
My father's name is Pietro and my grandfather's is Luigi, and his father's name is Pietro again.
I don't know if I have relatives around the world, but I can say that Cassano Magnago is literally full of Luonis! It's the most common surname here!
I dare to think that Cassano is the place of origin of the surname.
I made very little araldic researches, but I found nothing... all this stuff makes me wonder if all of us are offspring of one and only first Luoni in Cassano (he had to be very prolific, by the way... ;-P).