Factory function to create a random sampling summary function.
Examples
if (FALSE) { # \dontrun{
summary_random_10 <- summary_random_sample(n = 10, seed = 42)
gt <- geotessera()
result <- gt$summarize_region(
region = bbox,
year = 2024,
summary_fns = list(samples = summary_random_10)
)
} # }