Unfolding primitives for the RustUse geometry workspace.
`use-unfolding` provides unfold-step and plan records that can later back polyhedral-net workflows.
```rust
use use_unfolding::{UnfoldingPlan, UnfoldingStep};
let plan = UnfoldingPlan::new(vec![UnfoldingStep::new(0, 1)]);
assert_eq!(plan.step_count(), 1);
```