Add Selective Repeat ARQ implementation in C++, Python, Go, Rust, or C

### 🌐 Task: Re-implement `04_Selective_Repeat` in another language

This directory already contains a working Java implementation of the `04_Selective_Repeat` concept.

You're invited to contribute the same logic in **another language** such as:

- C++
- Python
- Go
- Rust
- C

📁 Your code must go inside the existing folder:

```

src/04_Selective_Repeat/

```

### 🧠 Guidelines:
- Do not overwrite or remove the Java files.
- Ensure your code is clear, modular, and readable.
- Feel free to use sockets, threading, I/O, etc., depending on the protocol used.