added note about reflection in input handlers

Author: Jolanrensen

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/aggregation/aggregators/AggregatorInputHandler.kt

@@ -21,6 +21,7 @@ internal interface AggregatorInputHandler<in Value : Any, out Return : Any?> : A
      *
      * If the specific [ValueType] of the input is not known, but you still want to call [aggregate],
      * this function can be called to calculate it by getting the types of [values] at runtime.
+     * This is heavy because it uses reflection on each value.
      */
     fun calculateValueType(values: Sequence<Value?>): ValueType
 

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/aggregation/aggregators/inputHandlers/AnyInputHandler.kt

@@ -33,6 +33,7 @@ internal class AnyInputHandler<in Value : Any, out Return : Any?> : AggregatorIn
      *
      * If the specific [ValueType] of the input is not known, but you still want to call [aggregate],
      * this function can be called to calculate it in terms of inheritance by getting the types of [values] at runtime.
+     * This is heavy because it uses reflection on each value.
      */
     override fun calculateValueType(values: Sequence<Value?>): ValueType {
         var hasNulls = false

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/aggregation/aggregators/inputHandlers/NumberInputHandler.kt

@@ -132,6 +132,7 @@ internal class NumberInputHandler<out Return : Any?> : AggregatorInputHandler<Nu
      * If the specific [ValueType] of the input is not known, but you still want to call [aggregate],
      * this function can be called to calculate it in terms of [number unification][UnifyingNumbers]
      * by getting the types of [values] at runtime.
+     * This is heavy because it uses reflection on each value.
      *
      * @throws IllegalArgumentException if the input type is not [Number]`(?)` or a primitive number type.
      * @return The (primitive) unified number type of the input values.