internal/pkg: expose cure whence

Useful for cure determinism validation of KindExec.

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

internal/pkg/archive_test.go

@@ -186,7 +186,7 @@ func TestArchiveArtifact(t *testing.T) {
 			cureMany(t, c, []cureStep{
 				{"sample", pkg.NewArchive(
 					pkg.NewFile("", buf.Bytes()),
-				), ignorePathname, expectsFS(want), nil},
+				), ignorePathname, expectsFS(want), pkg.WNew, nil},
 			})
 		}, expectsFS{
 			".": {Mode: fs.ModeDir | 0700},