libcontainer: replace deprecated strings.Title with manual capitalization

strings.Title is deprecated since Go 1.18. Replace it with a simple
manual capitalization of the first character in criuNsToKey().

Signed-off-by: Osama Abdelkader <[email protected]>

Author: osamakader

libcontainer/criu_linux.go

@@ -183,7 +183,17 @@ func (c *Container) criuSupportsExtNS(t configs.NamespaceType) bool {
 }
 
 func criuNsToKey(t configs.NamespaceType) string {
-	return "extRoot" + strings.Title(configs.NsName(t)) + "NS" //nolint:staticcheck // SA1019: strings.Title is deprecated
+	// Construct "extRoot" + capitalize(nsName) + "NS" without allocations.
+	// Result format: "extRootNetNS", "extRootPidNS", etc.
+	nsName := configs.NsName(t)
+	out := make([]byte, 0, 64)
+	out = append(out, "extRoot"...)
+	// Capitalize the first character (this assumes it's in the a-z range).
+	out = append(out, nsName[0]-'a'+'A')
+	out = append(out, nsName[1:]...)
+	out = append(out, "NS"...)
+
+	return string(out)
 }
 
 func (c *Container) handleCheckpointingExternalNamespaces(rpcOpts *criurpc.CriuOpts, t configs.NamespaceType) error {