Is your feature request related to a problem or challenge? Please describe what you are trying to do.

Currently DataType::Union has no protection against the same type ID appearing multiple times in its DataType.

Describe the solution you'd like

We should probably validate that the type_ids are unique, and prevent constructing an invalid DataType

Describe alternatives you've considered

We could not do this, much like currently permit invalid DataType::Decimal #2362

Additional context