Feature request: Add option to not display negative y-axis tick labels

[pli9]

There are some scenarios where the lower and upper y-limits need to be set manually, which may go into the negative values. Here is an example:

dat <- data.frame(
  month = seq(as.Date('2024-01-01'), length.out = 24, by = "month"),
  den = rpois(24, lambda = 5)
)
dat$num <- sapply(dat$den, function(x) rbinom(1, x, 0.25))
controlcharts::spc(
  data = dat,
  numerators = num,
  denominators = den,
  labels = num,
  keys = month,
  spc_settings = list(chart_type = "p"),
  y_axis_settings = list(
    ylimit_l = -20,
    ylimit_u = 100
  ),
  label_settings = list(
    label_position = "bottom",
    label_line_max_length = 30
  )
)

Which generates the following chart:

It would be useful to be able to toggle off any negative tick labels, so these don't show up on the y-axis.