Lazily register slider_plus() and slider_minus() methods

[DavisVaughan]

Joint PR with r-lib/slider#184

• Bump required slider version in DESCRIPTION to CRAN version
• Bump required slider version in skip_if_not_installed() to CRAN version
• Remove slider Remote

library(clock)
library(slider)

i <- date_build(2019, 1, c(1, 3, 4, 5, 7, 8))

slide_index(i, i, identity, .before = duration_days(2))
#> [[1]]
#> [1] "2019-01-01"
#> 
#> [[2]]
#> [1] "2019-01-01" "2019-01-03"
#> 
#> [[3]]
#> [1] "2019-01-03" "2019-01-04"
#> 
#> [[4]]
#> [1] "2019-01-03" "2019-01-04" "2019-01-05"
#> 
#> [[5]]
#> [1] "2019-01-05" "2019-01-07"
#> 
#> [[6]]
#> [1] "2019-01-07" "2019-01-08"

^{Created on 2022-11-10 with reprex v2.0.2.9000}