feat(stats): collect CDN access logs and publish download statistics

Add an hourly download-stats pipeline that reads the cran-rpkgs Bunny
access logs into a download_stats schema in the build metadata database
and publishes aggregated counts to /stats/downloads.json for the
rpkgs.com /stats page.

- Classify each request (download, index, redirect reason, probe, noise)
  mirroring the edge router, and split cloud/CI networks from the rest.
- De-duplicate downloads per client, package version and day, and key
  clients on a salted HMAC so no IP is stored or published.
- Exclude our own CI runners and record run windows to show gaps.
- Declare the zone's logging settings and allow CORS for JSON.

local/missing-cran-packages.R

@@ -42,14 +42,14 @@ files <- s3fs::s3_dir_ls(sprintf(
   "devxy-r-package-binaries-hel1/arm64/alpine320/latest/src/contrib"
 ))
 
-files_b = basename(files)
-files_b_split = sapply(strsplit(basename(files_b), "_"), function(x) x[1])
+files_b <- basename(files)
+files_b_split <- sapply(strsplit(basename(files_b), "_"), function(x) x[1])
 
 cran_pkgs <- tools::CRAN_package_db() |>
   filter(`Date/Publication` <= "2025-01-25") |>
   pull(Package)
 
-pkgs = setdiff(cran_pkgs, files_b_split)
+pkgs <- setdiff(cran_pkgs, files_b_split)
 formatted_pkgs <- gsub(
   '"',
   "'",