code: public static Resource.Provider group(Resource.Provider... providers) {
          return group(() -> Arrays.stream(providers));
      }
docs: Group ResourceProviders together into one resources Resource Provider.
  <p>
  {@code
  Resource.Provider providerA = Kute.directoryProvider(new File("images/"));
  Resource.Provider classpathProvider = Kute.getDefaultProvider();
  Resource.Provider provider = Kute.group(providerA, classpathProvider);
  }
  
  @param providers The resource providers to group.
  @return A resource provider that providers resources for all the given resource providers.