Move client to subpackage

Signed-off-by: Derek McGowan <derek@mcg.dev>

client/diff.go

@@ -0,0 +1,35 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package client
+
+import (
+	diffapi "github.com/containerd/containerd/v2/api/services/diff/v1"
+	"github.com/containerd/containerd/v2/diff"
+	"github.com/containerd/containerd/v2/diff/proxy"
+)
+
+// DiffService handles the computation and application of diffs
+type DiffService interface {
+	diff.Comparer
+	diff.Applier
+}
+
+// NewDiffServiceFromClient returns a new diff service which communicates
+// over a GRPC connection.
+func NewDiffServiceFromClient(client diffapi.DiffClient) DiffService {
+	return proxy.NewDiffApplier(client).(DiffService)
+}