Flagged in https://github.com/NixOS/nixpkgs/pull/376365#discussion_r1976613767.

This now properly restores the .nar extension.

After final improvements to the official formatter implementation,
this commit now performs the first treewide reformat of Nix files using it.
This is part of the implementation of RFC 166.

Only "inactive" files are reformatted, meaning only files that
aren't being touched by any PR with activity in the past 2 months.
This is to avoid conflicts for PRs that might soon be merged.
Later we can do a full treewide reformat to get the rest,
which should not cause as many conflicts.

A CI check has already been running for some time to ensure that new and
already-formatted files are formatted, so the files being reformatted here
should also stay formatted.

This commit was automatically created and can be verified using

    nix-build https://github.com/infinisil/treewide-nixpkgs-reformat-script/archive/a08b3a4d199c6124ac5b36a889d9099b4383463f.tar.gz \
      --argstr baseRev b32a0943687d2a5094a6d92f25a4b6e16a76b5b7
    result/bin/apply-formatting $NIXPKGS_PATH

Derivations affected by this patch set `__structuredAttrs = true;` and
provide their own `builder`, i.e. it's necessary to `source .attrs.sh`.

Rather than adding even more `if`-`source` monstrums, I decided to
modify all of those derivations to use `buildCommand` or `runCommand`,
without `builder` being set.

Then, `$stdenv/setup` is sourced already and as a result it's safe to
assume that `NIX_ATTRS_JSON_FILE`/`NIX_ATTRS_SH_FILE` point to a usable
location both in a build and a shell session.