internal/pkg: support tarball compressed via bzip2

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pkg/tar.go

@@ -3,6 +3,7 @@ package pkg
 import (
 	"archive/tar"
 	"bytes"
+	"compress/bzip2"
 	"compress/gzip"
 	"context"
 	"encoding/binary"
@@ -21,6 +22,8 @@ const (
 	TarUncompressed = iota
 	// TarGzip denotes a tarball compressed via [gzip].
 	TarGzip
+	// TarBzip2 denotes a tarball compressed via [bzip2].
+	TarBzip2
 )
 
 // A tarArtifact is an [Artifact] unpacking a tarball backed by a [File].
@@ -100,6 +103,10 @@ func (a *tarArtifact) Cure(c *CureContext) (err error) {
 		}
 		break
 
+	case TarBzip2:
+		tr = io.NopCloser(bzip2.NewReader(tr))
+		break
+
 	default:
 		return os.ErrInvalid
 	}