chore(pumpkin-core): Update cached predicate when known to not be satisfied

[ImkoMarijnissen]

This PR does 3 things:

1. When a nogood is created, the cached predicate points to the other watched predicate.
2. When a new watcher is found, the cached predicate is updated to be the other watched predicate (which is known to not be falsified, as it would otherwise have never looked for a new watcher).
3. Registers the PredicateId directly, instead of looking up the Predicate, and then afterwards looking up the PredicateId again.