Release v4.121.1

Fixed

• Generated code no longer silently leaves out a validation rule whose kind Stage does not know. The renderer, the specification executor and the semantic host now refuse such a model with STAGE-ESM-005, naming the rule kind, instead of rendering or running it without that rule. (part of #448)
• The default sandbox engine (cratis run without the semantic engine) now refuses a model that uses an unknown rule kind, with a clear reason, instead of ignoring the rule. The rules it already documents as not enforced are unchanged. (part of #448)