Converts district names to lowercase, URL-safe slugs suitable for use in district landing page URLs. SC districts use "County ##" format (e.g., "Aiken 01", "Anderson 02"). Collisions are resolved by appending the district_id.
Examples
slugify_district("Charleston 01")
#> [1] "charleston-01"
# "charleston-01"
slugify_district("Greenville 01")
#> [1] "greenville-01"
# "greenville-01"
slugify_district(c("Anderson 01", "Anderson 02"))
#> [1] "anderson-01" "anderson-02"
# c("anderson-01", "anderson-02")