Add unit tests for config

**Feature request**
It would be great to have caching for handlers.

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

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

No file or test path is named. Start by locating the configuration handling and handler entry points, then determine how caching should be applied when enable_caching is true. Done means the new option defaults to false, handler caching works when enabled, and unit tests cover the configuration behavior.

Written by the indexing model from the issue text.