Constructs a validated style object for use with table_summary().
Examples
sm_style(left_col = "blue_bold", right_col = "green", title = "bold")
#> <tabstats_style / sm_style>
#> left_col: "blue_bold"
#> right_col: "green"
#> title: "bold"
sm_style(left_col = \(x) cli::col_red(x), sep = "|")
#> <tabstats_style / sm_style>
#> left_col: <function>
#> sep: "|"
