bandwidth-throttle test worker

Run the SAME commands against your feature-on and feature-off zones and compare.

Download (measured client-side by curl):
  curl -s -o /dev/null -w 'dl_Bps=%{speed_download} time=%{time_total}\n' \
    'https://email.speedcf.com/download?mb=50'

Upload (measured client-side; server view is in the JSON response):
  head -c 52428800 /dev/urandom > /tmp/blob
  curl -s --data-binary @/tmp/blob -H 'content-type: application/octet-stream' \
    -w '\nul_Bps=%{speed_upload} time=%{time_total}\n' 'https://email.speedcf.com/upload'

Notes:
  - Size the payload so the transfer runs >= ~15-20s at your configured rate
    (e.g. rate 1 MiB/s -> mb=50). ?bytes=N also works on /download.
  - Run from a host whose real bandwidth >> the cap.
  - Do NOT pass --compressed; let curl omit Accept-Encoding.
  - The throttle is per-request: concurrent requests each get the full rate.