ModelID

Model IDs are represented internally using Int but only the positive part, so the maximum amount of simultaneous models is about 2 billion (we should find a way to use UInt). It is recommended to use a String (base36) externally.

Implementation details: We first used UInt, but it seems that there is a problem when making this @JvmInline and value class in combination with ULong and UInt (see KT-69674).

NOTE: If you make any change to this: clean build, and verify how a relation is serialized ("value" may appear). (If you use IntelliJ's database tool, double check that you actually see the difference, you may have to delete/refresh)