pkg/cri: replace some fmt.Sprintfs with strconv

Teeny-tiny optimizations:

    BenchmarkSprintf-10       37735996    32.31  ns/op  0 B/op  0 allocs/op
    BenchmarkItoa-10         591945836     2.031 ns/op  0 B/op  0 allocs/op
    BenchmarkFormatUint-10   593701444     2.014 ns/op  0 B/op  0 allocs/op

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

pkg/cri/server/container_create_windows.go

@@ -18,7 +18,6 @@ package server
 
 import (
 	"errors"
-	"fmt"
 	"strconv"
 
 	imagespec "github.com/opencontainers/image-spec/specs-go/v1"
@@ -147,9 +146,8 @@ func snapshotterOpts(snapshotterName string, config *runtime.ContainerConfig) ([
 	case "windows":
 		rootfsSize := config.GetWindows().GetResources().GetRootfsSizeInBytes()
 		if rootfsSize != 0 {
-			sizeStr := fmt.Sprintf("%d", rootfsSize)
 			labels := map[string]string{
-				"containerd.io/snapshot/windows/rootfs.sizebytes": sizeStr,
+				"containerd.io/snapshot/windows/rootfs.sizebytes": strconv.FormatInt(rootfsSize, 10),
 			}
 			opts = append(opts, snapshots.WithLabels(labels))
 		}