Formats numeric values as percentages with specified decimal places.
Examples
format_percentage(0.5, digits = 1) # Returns "50.0%"
#> [1] "50.0%"
format_percentage(c(0.123, 0.456, 0.789), digits = 1) # c("12.3%", "45.6%")
#> [1] "12.3%" "45.6%" "78.9%"