`iv_diff()`

[DavisVaughan]

Something like this:

iv_diff <- function(x) {
  if (!all(vctrs::vec_detect_complete(x))) {
    # Improve this
    rlang::abort("Can't have incomplete values")
  }
  
  # Let iv() handle `start < end`?
  
  size <- vctrs::vec_size(x)
  
  start <- rlang::seq2(1L, size - 1L)
  end <- rlang::seq2(2L, size)
  
  start <- vctrs::vec_slice(x, start)
  end <- vctrs::vec_slice(x, end)
  
  iv(start, end)
}

Inspired by something like https://stackoverflow.com/questions/72062077/remove-overlaps-from-lubridate-intervals