Purge buildx cache

You’re stuck building multi‑platform Docker images with buildx and have run out of hard‑drive space? You’ve tried every tutorial, running docker system prune --volumes, yet the huge buildx volume is still alive? Run docker buildx_buildkit_strange_name0 buildctl prune to clean that container’s caches properly and free up some space, without stopping the container or doing an rm -r you might regret.