`plotluck.multi()`is not robust against variables starting with a digit

[Christophe-Regouby]

Current behavior

Depending of the variable name characters, plotluck() may wrongly fail with unexpected_input error. Variable name starting with a digit will make plotluck fails with

Error in parse(text = call.str) : <text>:1:932: unexpected input
1: ),axis.text.y=element_blank(),strip.background=element_blank(),strip.text=element_blank(),panel.grid.major=element_blank(),panel.grid.minor=element_blank(),axis.title.x=element_text(size=rel(0```


# Expected behavior
Allow variable names starting with a digit

# ReprEx
``` r
library(plotluck)
library(dplyr)
#> 
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#> 
#>     filter, lag
#> The following objects are masked from 'package:base':
#> 
#>     intersect, setdiff, setequal, union
library(gapminder)
gapminder <- gapminder |> rename(`1_year` = "year")
plotluck(gapminder, .~1)
#> Error in parse(text = call.str): <text>:1:932: unexpected input
#> 1: ),axis.text.y=element_blank(),strip.background=element_blank(),strip.text=element_blank(),panel.grid.major=element_blank(),panel.grid.minor=element_blank(),axis.title.x=element_text(size=rel(0
#> 

^{Created on 2025-01-29 with reprex v2.1.1}