Affine-space helpers for the RustUse geometry workspace.
`use-affine` starts with small affine combination helpers rather than a full affine algebra system.
```rust
use use_affine::affine_combination_2d;
use use_point::Point2;
let midpoint = affine_combination_2d(Point2::new(0.0, 0.0), Point2::new(4.0, 2.0), 0.5);
assert_eq!(midpoint, Point2::new(2.0, 1.0));
```