Make retry handlers static methods

Convert handle_network_failure and handle_download_failure from instance methods to static methods. Hardcode retry params (max_retries, delays) instead of using instance state. Improves testability and removes implicit dependencies.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

tests/unit/test_template_helpers.py

@@ -30,7 +30,7 @@ class TestTemplateHelpers:
         assert context["request"] == request
         assert context["title"] == "Test Title"
         assert context["app_name"] == "Aniworld Download Manager"
-        assert context["version"] == "1.0.1"
+        assert context["version"] == "v1.3.6"
 
     def test_get_base_context_default_title(self):
         """Test that default title is used."""