update `ext` script (#986)

Arch & Artix already have the `libarchive` pkg, which contains `bsdtar`.
So lets just use it, since its superior, faster, it also has easier syntax, and it auto-detects the compression.
btw the .tar.zst was wrong anyhow, so if u wont merge this, dont forget to fix that. from the manual:
```
 -I, --use-compress-program=COMMAND
        Filter data through COMMAND.  It must accept the -d option, for decompression.  The argument can contain command line options.
.....
--zstd Filter the archive through zstd(1).
```

0 files changed, 0 insertions, 0 deletions