chore: Remove macOS metadata from test data tarballs (#1534)

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Remove AppleDouble files (`._*`, `.__*`) and macOS extended attributes
from test data tarballs.

The macOS metadata was handled in two ways:

  1. AppleDouble files (._*, .__*) - Explicitly deleted:
  find "$name" -name '._*' -delete
  find "$name" -name '.__*' -delete

  2. Extended attributes (LIBARCHIVE.xattr.*) - Automatically stripped:
When extracting on Linux, the macOS extended attributes (stored in PAX
headers) are ignored:
tar: Ignoring unknown extended header keyword
'LIBARCHIVE.xattr.com.apple.provenance'
tar: Ignoring unknown extended header keyword
'LIBARCHIVE.xattr.com.apple.quarantine'

This is what Claude code came up with:

```
  1. Identified affected files
  for f in *.tar.zst; do
    tar --zstd -tvf "$f" 2>&1 | grep -E '/\._|LIBARCHIVE\.xattr'
  done
  Found 25 tarballs containing macOS AppleDouble files (._*, .__*) and extended attributes.

  2. Cleaned each tarball
  for tarball in *.tar.zst; do
    name="${tarball%.tar.zst}"

    # Extract
    tar --zstd -xf "$tarball"

    # Remove AppleDouble files
    find "$name" -name '._*' -delete
    find "$name" -name '.__*' -delete

    # Recompress
    tar --zstd -cf "$tarball" "$name"

    # Cleanup
    rm -rf "$name"
  done

```

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Tests pass and opening up a tarball now contains no artifacts

Author: DrakeLin