`source.url = XXX.tar.gz` 852 times slower than `cli untar`

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### Please fill out the following:
- **Platform:**
- Linux.

ArchLinux + nixpkgs

- **LuaRocks version:**
- 3.13.0

- **Configuration file:**
- Please try to produce with the default configuration.
- If you cannot reproduce with the default configuration, please try to find
the minimal configuration to reproduce.
- Upload the config to a pastebin such as gist.github.com.

- **LuaRocks output from when the issue occurred:**
- Use the `--verbose` flag.

- **Description:**
- The steps you took in plain English to reproduce the problem.

# bug

`source.url = XXX.tar.gz` 852 times slower than `cli untar`

## unexpected

`source.url = XXX.tar.gz` takes 28.9s, which is

- 51.571174377224196 times slower than `source.url = 'git+http://XXX'`

- 56.27766990291262 times slower than `source.url = 'XXX.zip'`

- 852.4411764705882 times slower than `cli untar`

```lua
source = {
url = 'http://example.com/repo/archive/commit.tar.gz',
...
}
```

```console
$ rm -rf ~/.luarocks
$ time luarocks install xxx
...
real 0m28.983s
user 0m10.908s
sys 0m17.665s
```

```lua
function tar.untar(filename, destdir)
...

-- FIXME: 28s
while true do
...
end

...
```

## expected

- `source.url = 'git+http://XXX'` takes 0.562s

- `source.url = 'XXX.zip'` takes 0.515s

- `cli untar` takes 0m0.034s

## git

```lua
source = {
url = 'git+http://example.com/repo.git',
...
}
```

```console
$ rm -rf ~/.luarocks
$ time luarocks install xxx
...
real 0m0.562s
user 0m0.488s
sys 0m0.193s
```

## zip

```lua
source = {
url = 'http://example.com/repo/archive/commit.zip',
...
}
```

```console
$ rm -rf ~/.luarocks
$ time luarocks install xxx
...
real 0m0.515s
user 0m0.167s
sys 0m0.177s
```

## tgz

```console
$ du -sh /tmp/commit.tar; time tar -xf /tmp/commit.tar -C "$(mktemp -d)"
12M /tmp/commit.tar

real 0m0.034s
user 0m0.008s
sys 0m0.026s
```

## workaround

Use commit.zip instead of commit.tar.gz

## suggestion

Try `cli untar` first.

## related

Use commit tarball as workaround for

https://github.com/luarocks/luarocks/issues/569

Start by reproducing the Linux LuaRocks 3.13.0 timings with `luarocks install xxx`, then inspect the `tar.untar(filename, destdir)` function mentioned in the issue. Compare its extraction path with `cli untar` and verify that `.tar.gz` installation approaches the command-line extraction time without breaking archive handling.

Written by the indexing model from the issue text.