Write an Rcpp function `allgt(x, y)` which takes a numeric vector `x` (assume there are no missing values) and a double `y` that checks if all the elements in `x` are greater than `y`. Benchmark the RCpp function and the R code with vectors of different proportions of positive numbers, e.g. `sample(c(1L, -1L), 1e5, prob = c(1-p, p), replace = TRUE)` for `p = 0.5, 0.05`, `0.005` and `0`. Comment on what you observe.