Concrete interval type tests only indirectly rely on same TypeOperations than tested types

[Whathecode]

To remove redundancy in setting up unit tests for each concrete Interval type (e.g. IntInterval implementing Interval<Int, UInt>), BasicTypeIntervalsTest.kt uses an inline function to retrieve the type operations for the type parameters (using getBasicTypeOperationsFor()).

This manually needs to be kept in sync if the operations ever change.

Is there a way to directly retrieve the matching TypeOperations from the concrete types? Maybe through a common factory interface on the companion objects?

[Whathecode]

TypeOperations are now statically linked to concrete interval types as an Operations property of the newly introduced IntervalTypeOperations in their companion objects.

This allows reusing these in unit tests to instantiate Interval through it's base class which takes the IntervalTypeOperations parameter.

By doing so, this doesn't test the concrete type interval constructors, but given that these simply forwards the same parameters to the base Interval class there is little risk of mistakes here. Furthermore, these will likely be covered by unit tests once we add API convenience functions such as Byte.intervalTo.