An `Ord`-based, array-backed set and map type.
`OrdSet<T, N>` is a set type backed by a `[T; N]` array. It behaves much like a
`BTreeSet`, but with a static size and no nodes. It's all a single array. This
means that insertions into the middle can be very slow. This also allows
getting the entire set as a sorted slice.
`OrdMap<K, V, N>` is a map type backed by a `[K; N]` and a `[V; N]` array. It
has most of the same considerations as `OrdSet`, but for a map type.