tiny API fixes for kotlin 2.2 in core

Author: Jolanrensen

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/api/groupBy.kt

@@ -115,4 +115,5 @@ public class ReducedGroupBy<T, G>(
 }
 
 @PublishedApi
-internal fun <T, G> GroupBy<T, G>.reduce(reducer: Selector<DataFrame<G>, DataRow<G>?>) = ReducedGroupBy(this, reducer)
+internal fun <T, G> GroupBy<T, G>.reduce(reducer: Selector<DataFrame<G>, DataRow<G>?>): ReducedGroupBy<T, G> =
+    ReducedGroupBy(this, reducer)

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/api/pivot.kt

@@ -268,7 +268,8 @@ public class ReducedPivot<T>(
 }
 
 @PublishedApi
-internal fun <T> Pivot<T>.reduce(reducer: Selector<DataFrame<T>, DataRow<T>?>) = ReducedPivot(this, reducer)
+internal fun <T> Pivot<T>.reduce(reducer: Selector<DataFrame<T>, DataRow<T>?>): ReducedPivot<T> =
+    ReducedPivot(this, reducer)
 
 @PublishedApi
 internal inline fun <T> Pivot<T>.delegate(crossinline body: PivotGroupBy<T>.() -> DataFrame<T>): DataRow<T> =

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/io/html.kt

@@ -533,7 +533,7 @@ public fun <T> DataFrame<T>.toHTML(
     configuration: DisplayConfiguration = DisplayConfiguration.DEFAULT,
     cellRenderer: CellRenderer = DefaultCellRenderer,
     getFooter: (DataFrame<T>) -> String? = { "DataFrame [${it.size}]" },
-) = toHtml(configuration, cellRenderer, getFooter)
+): DataFrameHtmlData = toHtml(configuration, cellRenderer, getFooter)
 
 @Deprecated(TO_STANDALONE_HTML, ReplaceWith(TO_STANDALONE_HTML_REPLACE), DeprecationLevel.ERROR)
 public fun <T> DataFrame<T>.toStandaloneHTML(