Add real-time versions?

Nobody has claimed this yet.

I'm really not sure it's worth the trouble, but we could improve the amortized times to worst-case using scheduling. Okasaki's scheme uses a separate schedule, which doesn't seem terribly compact, and his analysis is rather tricky. I think we can do something a bit simpler. The debit invariant allows one debit on the child of a `Skip` node, and no debits anywhere else. We can arrange to force a node as soon as its parent changes from a `Skip` to a `Cons`. To accomplish that, we can arrange to always have access to the first `Skip` node by linking them together.

```haskell
data Scheduled rk a = forall xxrk x. Scheduled !(BinomForest rk a) (BinomForest xxrk x)
data BinomForest rk a
= Nil
-- The second field points to the next Skip node, or Nil if there is none.
| forall xxrk x. Skip (BinomForest (Succ rk) a) (BinomForest xxrk x)
| Cons {-# UNPACK #-} !(BinomTree rk a) !(BinomForest (Succ rk) a)
```

This gives a somewhat segmented flavor. Another option, of course, might be to use a segmented number system. Doing that with nested types will require type-aligned (nonempty) lists; I'm not sure how complicated it will get. And then there are also skew binomial heaps, which I don't really understand yet.

Start by comparing the proposed Scheduled and BinomForest definitions with the current priority-queue implementation. Evaluate the linked Skip-node scheduling approach against segmented number systems and skew binomial heaps, then establish whether a real-time implementation can provide worst-case bounds without excessive complexity.

Written by the indexing model from the issue text.