docs(core): update `find()` and `rfind()` examples [find()](https://doc.rust-lang.org/std/iter/trait.Iterator.html) has a missing example. In the docs there is mention of an example with double reference but it doesn't exist. <img width="1476" height="1229" alt="image" src="https://github.com/user-attachments/assets/b99062ed-3a47-4b87-8e0c-58afd7de1332" /> [rfind()](https://doc.rust-lang.org/core/iter/trait.DoubleEndedIterator.html#method.rfind) is also very similar to `find()`, however it has the double reference example and no owned value example like `find()` does. <img width="1473" height="1163" alt="image" src="https://github.com/user-attachments/assets/7977ae5c-9888-4513-8dfc-a7c03c7ef072" /> This commit adds the missing examples and making them look consistent.