Move protobuf package under pkg

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

core/runtime/v2/task_manager.go

@@ -30,9 +30,9 @@ import (
 	apitypes "github.com/containerd/containerd/v2/api/types"
 	"github.com/containerd/containerd/v2/core/runtime"
 	"github.com/containerd/containerd/v2/internal/cleanup"
+	"github.com/containerd/containerd/v2/pkg/protobuf/proto"
 	"github.com/containerd/containerd/v2/pkg/timeout"
 	"github.com/containerd/containerd/v2/plugins"
-	"github.com/containerd/containerd/v2/protobuf/proto"
 )
 
 func init() {