backup: hide files from status which are read completely but not saved

As the FileSaver is asynchronously waiting for all blobs of a file to be
stored, the number of active files is higher than the number of files
from which restic is reading concurrently. Thus to not confuse users,
only display files in the status from which restic is currently reading.

internal/archiver/file_saver_test.go

@@ -60,6 +60,7 @@ func TestFileSaver(t *testing.T) {
 	defer cleanup()
 
 	startFn := func() {}
+	completeReadingFn := func() {}
 	completeFn := func(*restic.Node, ItemStats) {}
 
 	testFs := fs.Local{}
@@ -78,7 +79,7 @@ func TestFileSaver(t *testing.T) {
 			t.Fatal(err)
 		}
 
-		ff := s.Save(ctx, filename, filename, f, fi, startFn, completeFn)
+		ff := s.Save(ctx, filename, filename, f, fi, startFn, completeReadingFn, completeFn)
 		results = append(results, ff)
 	}