Add advanced C++ topics — Object Slicing, Copy Elision & More

[gvatsal60]

Hi 👋 @methylDragon,

First off — I just wanted to say I absolutely loved the current C++ content! 😍
It’s been super helpful and well-structured — thank you for putting it together 🙌

That said, I think it would be awesome to include some more advanced C++ topics, such as:

🧩 Object Slicing — explanation with class inheritance examples

⚡ Copy Elision / Return Value Optimization (RVO) — modern compiler optimizations

These topics are super useful for understanding what’s going on under the hood in modern C++.

Thanks again for the amazing work! 💙
Keep it up 🚀