Resource Management and the RAII Idiom

Explain the RAII (Resource Acquisition Is Initialization) principle as a core C++ idiom.

Implement a simple RAII wrapper for a file handle to ensure cleanup upon scope exit.

Analyze stack unwinding during exception handling and how it enables RAII.

Use `std::unique_ptr` for exclusive ownership and explain its move-only semantics.

Implement a basic reference-counted smart pointer to understand the shared ownership mechanism.

Use `std::weak_ptr` to break circular references involving `std::shared_ptr`.

Refactor C-style code using raw pointers and manual memory management to modern C++ using smart pointers.