NonZero Int type support

[MiguelX413]

Implementing FromPyObject for NonZero int types.
I think it'd be a great minor feature, but far from necessary.

[davidhewitt]

Agreed, I'd be very happy if someone was interested in adding this.

I've also wanted support for the ordered-float crate in the past for NotNan types, so would happily accept that as an optional feature like our other thirdparty conversion features.

[MiguelX413]

Agreed, I'd be very happy if someone was interested in adding this.

I've also wanted support for the ordered-float crate in the past for NotNan types, so would happily accept that as an optional feature like our other thirdparty conversion features.

That sounds like a great idea! I'll see if I'm at a level good enough to add them myself.

[davidhewitt]

Thanks for the interest! Have a look at the contents in https://github.com/PyO3/pyo3/tree/main/src/conversions.

I'd suggest putting these in conversions/std/num.rs and conversions/ordered_float.rs. I'd do them as separate PRs to keep reviews simpler and easier to track history.

Please ask if there are any parts which seem unclear which you'd like clarification.