[General: Slow Testing Exercises] Exercises that have Slow Running Tests that Time Out in the UI

This is an open issue for Exercises that have reasonable solutions that "time out" under test in the UI.

To be clear -- this is not for exercises that time out due to inefficient code, but ones that reasonably pass in in the runner locally or in docker, but take too long in the UI once the containers are spun up and configured.

For now, we need to flag these as "slow", so that they don't run on the website and unnecessarily take up resources.

Please add any additional exercises you think fit this criteria. Thanks!

- [ ] Palindrome Products
- [ ] Pythagorean Triplet