move readCloserWrapper to be a test-utility

It's only used in tests now, so move it there.

Signed-off-by: Sebastiaan van Stijn <[email protected]>

Author: thaJeztah

Diff for: archive.go

@@ -132,18 +132,6 @@ func DetectCompression(source []byte) compression.Compression {
 	return compression.Detect(source)
 }
 
-type readCloserWrapper struct {
-	io.Reader
-	closer func() error
-}
-
-func (r *readCloserWrapper) Close() error {
-	if r.closer != nil {
-		return r.closer()
-	}
-	return nil
-}
-
 // DecompressStream decompresses the archive and returns a ReaderCloser with the decompressed archive.
 //
 // Deprecated: use [compression.DecompressStream].

Diff for: diff_test.go

@@ -310,6 +310,18 @@ func TestApplyLayerWhiteouts(t *testing.T) {
 	}
 }
 
+type readCloserWrapper struct {
+	io.Reader
+	closer func() error
+}
+
+func (r *readCloserWrapper) Close() error {
+	if r.closer != nil {
+		return r.closer()
+	}
+	return nil
+}
+
 func makeTestLayer(paths []string) (_ io.ReadCloser, retErr error) {
 	tmpDir, err := os.MkdirTemp("", "graphdriver-test-mklayer")
 	if err != nil {