Converting Package to UPM

[omangbaheti]

This PR converts the project into a Unity Package Manager (UPM) compatible package, making it convenient for devs to clone the package directly into their Unity projects via UPM.

Changes Made

• Migrated all source code (C# Forms app and C++ code) to the src~ folder
• Rewrote package.json to comply with Unity's UPM format and enable sample importing
• Preserved existing functionality and project structure as much as possible

Testing

• Verified functionality on a Logitech G920 wheel
• All force feedback effects appear to work as expected

---

TODO:

• Update the changelog
• Update installation introductions in the readme