Understand, protect against, and benchmark possible overfitting

**Have you checked the [list of proposed rules](https://github.com/Benjamin-Lee/deep-rules/issues?q=is%3Aissue+is%3Aopen+label%3Arule) to see if the rule has already been proposed?**

- [X] Yes

**Feel free to elaborate, rant, and/or ramble.**

**Any citations for the rule?** (peer-reviewed literature preferred but not required)
- [DOI](doi.org/DOI_goes_here)

Start by reviewing the linked list of proposed rules to check for overlap. The issue currently contains only a placeholder for a DOI and no defined rule, scope, or benchmark; a complete proposal would need those details and supporting citations before implementation or manuscript work can be assessed.

Written by the indexing model from the issue text.