I would like to suggest to pass a slice of arrays with dimension defined as const generic. And instead of accepting dimensions as a number, use [usize; 2] with indices to use. I.e. to use first two values from each array (x and y), use [0, 1].
It would be more ergonomic and more efficient since libraries usually represent meshes as vector of arrays instead of vector of values.

Hi! Thanks a lot for implementing my suggestions in #5. I decided to try the crate, but noticed a few inconveniences with the API:

1. You now accept iterator for vertices which is quite convenient, but you require item to be &[f32; 2]. It's a problem when you actually have 3D coordinates and you trying to convert them into 2D:

positions.iter().map(|&[x, y, _]| &[x, y]);

I can't return &[x, y] from a closure. I would suggest to remove the reference (make it just [f32; 2]) or make turn it into an iterator over just f32. I would suggest the latter since it will be a little closer to how the JS version works.

2. You return triangles as Vec<[N; 3]>. But some crates, like Bevy, store them as just f32. I would suggest to return just Vec<N>. This way it will be more consistent with (1).

In the benchmark section, earcut-rs (0.4.1) - water_huge2 is 11.0k ms/i, which is almost 1000 times earcutr (0.4.3) - water_huge2 (10.90 ms/i).