Derive Macro MaybeHasNiche 

#[derive(MaybeHasNiche)]

use object_rainbow::{MaybeHasNiche, Size};

#[derive(Size, MaybeHasNiche)]
struct WithHole(bool, u8);

#[derive(Size, MaybeHasNiche)]
struct NoHole(u8, u8);

assert_eq!(Option::<WithHole>::SIZE, 2);
assert_eq!(Option::<NoHole>::SIZE, 3);