Add interactive string interop example with ownership and user flow

[shashu8660]

This PR adds an interactive string interoperability example between Rust and C++.

The example demonstrates:

• Passing strings from C++ to Rust using const char*
• Returning strings from Rust to C++ using CString
• Ownership transfer across the FFI boundary (Move, Forget, Own)
• Safe memory management and explicit deallocation
• Interactive user input flow

The example includes:

• Rust library exposing FFI functions
• C++ program handling user input and interaction
• run.sh script for building and running the example

This aligns with the string interop problem https://github.com/rustfoundation/interop-initiative/blob/main/problem-space/0002-string-interop.md & demonstrates safe handling of string ownership and memory across language boundaries

[teor2345]

Hi, I've already looked at your PR #30, we're just going to focus on one PR per person for now. After that PR is finished, we can decide what to do with this one.