Returns the names of all currently registered reduction operations.
Examples
head(registered_reductions())
#> [1] "Count" "GeoMean" "Max" "Mean"
#> [5] "Median" "Median_example"
register_reduction("Median_example", function(x, ...) median(x), overwrite = TRUE)
"Median_example" %in% registered_reductions()
#> [1] TRUE