`calc` issues in datasets with `duration` and `time_period`

When trying to `calc` variables to change type to `duration` or `time_period`, Trevas is silently dropping theses variables.

See [this example](https://github.com/InseeFr/Trevas/blob/develop/vtl-spark/src/test/java/fr/insee/vtl/spark/processing.engine/AggregateTest.java#L206), and uncomment to reproduce.