v3; defaults to pkgx^2; pure js rewrite #104

Job	Run time
install-pkgx (macos-latest)	5s
install-pkgx (ubuntu-latest)	12s
sudo-not-required	13s
usage-as-proxy	44s
eval-bash	12s
eval-posix-sh	12s
eval-zsh	26s
multiple-apply-is-ok	20s
no-dirs (/usr/local)	35s
sudo-required	12s
no-dirs (/usr/local/bin)	13s
linuxen (debian:buster-slim)	18s
upgrades	18s
linuxen (debian:bullseye-slim)	20s
linuxen (debian:bookworm-slim)	20s
linuxen (archlinux:latest)	20s
linuxen (ubuntu:focal)	21s
linuxen (ubuntu:jammy)	20s
linuxen (ubuntu:24.04)	19s
linuxen (ubuntu:24.10)	25s
linuxen (fedora:latest)	20s
	6m 45s

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