utils: put UniqueResource in utils namespace

... because everything in utils belong in that namespace.

Change-Id: I3b3f8f3b33163abd5090e3cf1a3f04971daba118
diff --git a/src/utils/UniqueResource.h b/src/utils/UniqueResource.h
index 34a4050..3af69ca 100644
--- a/src/utils/UniqueResource.h
+++ b/src/utils/UniqueResource.h
@@ -3,12 +3,14 @@
  *
  * Written by Jan Kundrát <jan.kundrat@cesnet.cz>
  *
-*/
+ */
 
 #pragma once
 
 #include <functional>
 
+namespace velia::utils {
+
 class UniqueResource {
 public:
     using Func = std::function<void()>;
@@ -34,3 +36,4 @@
 {
     return UniqueResource(std::move(init), std::move(cleanup));
 }
+}