feat: add combined server-client program in C++

[missonpaudel]

Combined Server-Client Program in C++

Describe your changes

This PR introduces a C++ program that combines both server and client functionalities in a single file. The user can choose whether to run the program as a server or client at runtime.

• The Server class initializes the server, accepts client connections, and handles communication.
• The Client class initializes the client, connects to the server, and handles message exchange.
• The program provides an interactive prompt for selecting either the server or client mode, then proceeds with the respective functionality.

This PR provides a basic example of how to implement a simple server-client architecture in C++ using object-oriented programming (OOP). It can be useful for educational purposes or as a base for more complex networking programs.

Checklist before requesting a review

• [x] If it is a core feature, I have added thorough tests.
• [x] My code follows the style guidelines of this project.
• [x] I have performed a self-review of my code.
• [x] I have commented my code, particularly in hard-to-understand areas.
• [x] I have made corresponding changes to the documentation.
• [x] I have only one commit (if not, squash them into one commit).
• [x] This PR is not a duplicate.

[axyut]

next time you open a pr, please add closes #xxxx closes #10 to auto close the issue that you worked on.