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/debug-packages-writing.R

@@ -1,7 +1,7 @@
 library(future)
 future::plan(multisession)
 future::plan(sequential)
-time = Sys.time()
+time <- Sys.time()
 files <- s3fs::s3_dir_ls(
   sprintf(
     "devxy-r-package-binaries-hel1/arm64/rhel9/latest/src/contrib/Archive"
@@ -54,8 +54,8 @@ curl::curl_download(
   "https://cran.devxy.io/amd64/rhel9/latest/src/contrib/PACKAGES.db",
   "PACKAGES.db"
 )
-con = DBI::dbConnect(RSQLite::SQLite(), "PACKAGES.db")
-df = DBI::dbReadTable(con, "packages")
+con <- DBI::dbConnect(RSQLite::SQLite(), "PACKAGES.db")
+df <- DBI::dbReadTable(con, "packages")
 
 cranlike:::write_packages_files("/tmp", "PACKAGES.db")
 
@@ -69,11 +69,11 @@ system("cat /tmp/PACKAGES | grep '^Package: digest' | wc -l")
 curl::curl_fetch_memory(
   "https://cloud.r-project.org/src/contrib/Meta/archive.rds"
 )
-remotes = readRDS(url(
+remotes <- readRDS(url(
   "https://cloud.r-project.org/src/contrib/Meta/archive.rds",
   "rb"
 ))
-packages = readRDS(url(
+packages <- readRDS(url(
   "https://cran.devxy.io/arm64/noble/latest/src/contrib/PACKAGES.rds",
   "rb"
 ))