Only markSimplified when we are sure the predicate is in fact simplified

[goodlyrottenapple]

Kore is currently is crashing for @bbyalcinkaya in komet, with:

CallStack (from HasCallStack):
  error, called at src/Kore/Internal/Predicate.hs:1091:5 in kore-0.1.76-9jTVMLO4n9YCl9sOQx8AFb:Kore.Internal.Predicate
  cannotSimplifyNotSimplifiedError, called at src/Kore/Internal/Predicate.hs:1120:36 in kore-0.1.76-9jTVMLO4n9YCl9sOQx8AFb:Kore.Internal.Predicate
  checkedSimplifiedFromChildren, called at src/Kore/Internal/Predicate.hs:1130:14 in kore-0.1.76-9jTVMLO4n9YCl9sOQx8AFb:Kore.Internal.Predicate
  markSimplified, called at src/Kore/Simplify/Not.hs:152:17 in kore-0.1.76-9jTVMLO4n9YCl9sOQx8AFb:Kore.Simplify.Not","error":"Unexpectedly marking term with NotSimplified children as simplified:
...

[goodlyrottenapple]

No change in KEVM

[jberthold]

Maybe still good to investigate this a bit more before we swallow the unexpected condition...
There was a bug report supplied on slack.