`queries.ml`: Detect if number is assigned multiple times in `order`

@Ang9876 observed if one makes a mistake and re-uses numbers (e.g., because @michael-schwarz added a new case in the middle breaking the assumption that numbers are increasing and the highest one is at the bottom), Goblint will still compile but then segfault upon running an analysis (probably because of the type-unsafe shenanigans going on in the query system). This took us a while to debug. Ideally, there would be some way to detect this at compile time.