Optionally fail for slow tests

In a number of projects we are adding in CI that will fail unit tests if they take longer than X e.g.
* https://github.com/bluesky/ophyd-async/issues/729
* https://github.com/DiamondLightSource/dodal/issues/1003
* https://github.com/DiamondLightSource/mx-bluesky/issues/663

Given this is used by lots of different repos we should put it in the template for people to use optionally.

先找出範本的 CI 與測試設定，然後比較連結專案對慢速測試的處理方式。當產生的專案可以選擇啟用可設定的慢速單元測試失敗門檻，且不影響將此選項維持停用的專案時，即表示完成。

由索引模型根據 Issue 內容生成。