broadcast & permute need to check that non-broadcast dims are the same for usize dims

[coreylowman]

Right now the broadcast/permute shape traits are implemented for any Dim, meaning they also apply to usize. This means it is possible to do:

use dfdx::prelude::*;

fn main() {
    let dev: Cpu = Default::default();

    let a: Tensor<(usize,), f32, _> = dev.zeros_like(&(3,));
    let b = a.broadcast_like::<_, Axis<0>>(&(2, 5));
    println!("{:?}", b);
}