repository: move Blob, Blobs and PackedBlob to pack package

This removes them from the public interface. The latter now only
provides the PackBlob interface, without being bound to the type used
internally by the pack package.

internal/repository/index_testutil_test.go

@@ -1,14 +1,15 @@
 package repository
 
 import (
+	"github.com/restic/restic/internal/repository/pack"
 	"github.com/restic/restic/internal/restic"
 )
 
 // BlobsInPack returns index entries for blobs stored in packID, sorted by offset.
-func BlobsInPack(repo *Repository, packID restic.ID) restic.Blobs {
-	var blobs restic.Blobs
+func BlobsInPack(repo *Repository, packID restic.ID) pack.Blobs {
+	var blobs pack.Blobs
 	for pb := range repo.idx.Values() {
-		if pb.PackID.Equal(packID) {
+		if pb.PackID().Equal(packID) {
 			blobs = append(blobs, pb.Blob)
 		}
 	}