Vendors the npm tarball + lockfile and wraps the `pi` binary with `fd` and
`ripgrep` on PATH. Also installs it on the m4 darwin host.
`buildNpmPackage` is pulled from `inputs.unstable` because nixos-25.11's
`prefetch-npm-deps-0.1.0` panics on cacache index entries that contain
either multiple lines or JSON values with embedded spaces (npm's
`accept: application/...; q=1.0, ...` headers). For this lockfile,
`@esbuild/netbsd-arm64` and `@rollup/rollup-linux-x64-musl` trigger
both conditions and `--map-cache` fails with `EOF while parsing a
string at line 1 column 369`. Fixed upstream in nixos-unstable, which
now uses `lines()` + `split_once('\t')`.
