[DF] Reduce Define jitting times

In my (very artificial) benchmark, I see a 15% reduction in jitting
time thanks to this change.

tree/dataframe/inc/ROOT/RDF/InterfaceUtils.hxx

@@ -373,8 +373,9 @@ void JitDefineHelper(F &&f, const ColumnNames_t &cols, std::string_view name, RL
    // share data after it has lazily compiled the code. Here the data has been used and the memory can be freed.
    delete customColumns;
 
+   // use unique_ptr<RCustomColumnBase> instead of make_unique<NewCol_t> to reduce jit/compile-times
    jittedCustomCol.SetCustomColumn(
-      std::make_unique<NewCol_t>(lm, name, std::move(f), cols, lm->GetNSlots(), newColumns));
+      std::unique_ptr<RCustomColumnBase>(new NewCol_t(lm, name, std::move(f), cols, lm->GetNSlots(), newColumns)));
 }
 
 /// Convenience function invoked by jitted code to build action nodes at runtime