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

It is beautiful:

i <- as.Date("1970-01-07") + 0:7
x <- clock::as_weekday(i)

slider::slide_index(
  .x = x,
  .i = i,
  .f = identity,
  .before = almanac::workdays(1),
  .after = almanac::workdays(1)
)
#> [[1]]
#> <weekday[2]>
#> [1] Wed Thu
#> 
#> [[2]]
#> <weekday[3]>
#> [1] Wed Thu Fri
#> 
#> [[3]]
#> <weekday[5]>
#> [1] Thu Fri Sat Sun Mon
#> 
#> [[4]]
#> <weekday[4]>
#> [1] Fri Sat Sun Mon
#> 
#> [[5]]
#> <weekday[4]>
#> [1] Fri Sat Sun Mon
#> 
#> [[6]]
#> <weekday[5]>
#> [1] Fri Sat Sun Mon Tue
#> 
#> [[7]]
#> <weekday[3]>
#> [1] Mon Tue Wed
#> 
#> [[8]]
#> <weekday[2]>
#> [1] Tue Wed

^{Created on 2022-11-09 with reprex v2.0.2.9000}