Improve api performance

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

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

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

No files, tests, or entry points are named. Start by locating the validation flow and configuration parsing, then determine where validation results could be cached and how the enable_caching option is represented. Done should include tests showing caching is disabled by default and that enabled caching improves repeated validation without changing results.

Written by the indexing model from the issue text.