Package-level declarations

NOTE: Normally in Interpoator we have a type T that defines the input and a type R that defines the output. However since the batch interpolator desires to allow the user to returnt he param function which takes a generic A (which is deinfed on the invoke/interploate functions) any R paramter defined on the InterpolatorBatching-level would need to somehow have this information. For example, if we wanted invoke/interploate to return some kind of Out then we would need to have a way to define this on the InterpolatorBatching interface. This would likely require some other assumptions such as the R (i.e. Out) parameter being a higher-order type Out<_> which is not even supported in Kotlin. So for now we will just assume that invoke and interpolate have the same type in the macro and treat whatever type comes out from invoke as the same type that comes out of interpolate.