Nesting `cli_ul` and/or `cli_ol`

[rundel]

Currently it appears that both of these list interfaces only support at most two levels of nesting. See the examples below for either ul, ol, or mixed cases:

test_ul = function(n = 2) {
  for(i in seq_len(n)) {
    cli::cli_ul()
    cli::cli_li(paste0("Level ",i))
  }
}

test_ul(2)
#> ● Level 1
#>   ◯ Level 2
test_ul(3)
#> ● Level 1
#>   ◯ Level 2
#>   ─ Level 3
test_ul(4)
#> ● Level 1
#>   ◯ Level 2
#>   ─ Level 3
#>   ─ Level 4

test_ol = function(n = 2) {
  for(i in seq_len(n)) {
    cli::cli_ol()
    cli::cli_li(paste0("Level ",i))
  }
}

test_ol(2)
#> 1. Level 1
#>   1. Level 2
test_ol(3)
#> 1. Level 1
#>   1. Level 2
#>   1. Level 3
test_ol(4)
#> 1. Level 1
#>   1. Level 2
#>   1. Level 3
#>   1. Level 4

test_ol_ul = function(n = 2) {
  for(i in seq_len(n)) {
    cli::cli_ol()
    cli::cli_li(paste0("Level ",2*i-1))
    
    cli::cli_ul()
    cli::cli_li(paste0("Level ",2*i))
  }
}

test_ol_ul(1)
#> 1. Level 1
#>   ● Level 2
test_ol_ul(2)
#> 1. Level 1
#>   ● Level 2
#>   1. Level 3
#>   ◯ Level 4
test_ol_ul(3)
#> 1. Level 1
#>   ● Level 2
#>   1. Level 3
#>   ◯ Level 4
#>   1. Level 5
#>   ─ Level 6

test_ul_ol = function(n = 2) {
  for(i in seq_len(n)) {
    cli::cli_ul()
    cli::cli_li(paste0("Level ",2*i-1))
    
    cli::cli_ol()
    cli::cli_li(paste0("Level ",2*i))
  }
}

test_ul_ol(1)
#> ● Level 1
#>   1. Level 2
test_ul_ol(2)
#> ● Level 1
#>   1. Level 2
#>   ◯ Level 3
#>   1. Level 4
test_ul_ol(3)
#> ● Level 1
#>   1. Level 2
#>   ◯ Level 3
#>   1. Level 4
#>   ─ Level 5
#>   1. Level 6

[gaborcsardi]

I suspect I introduced this bug recently. Thanks for the report!