Consider deprecating old routes API

**Feature request**
It would be great to have serialization for helpers.

**Use case**
Many users need this functionality for production deployments.

**Implementation idea**
Add a new config option `enable_serialization` with default `false`.

Start by reconciling the title about deprecating the old routes API with the body’s request for helper serialization. Then locate the configuration and helper-handling entry points, determine the intended behavior of enable_serialization (default false), and identify tests that should demonstrate serialization is enabled and disabled.

Written by the indexing model from the issue text.