License is inconsistent

### What Happened?

This repository contains two licenses—GPL 3 and LGPL 2.1.

### Steps to Reproduce

1. See README. It says the license is GPL 3
2. See any files in `src/`. These files says the license is LGPL 2.1

### Expected Behavior

The license should be unified to either of GPL or LGPL. Also, if we choose LGPL we should use its latest version 3.

### OS Version

N/A

### Software Version

N/A

### Log Output

_No response_

### Hardware Info

_No response_