Implemented a new feature: Ability to include more sirens within a vehicle

This feature allows vehicle developers to add more sirens to their vehicles that can be changed with a keybind while the sirens are active. More documentation on this feature is available in the pinned thread within Discussions.

- Minor compatibility change

- Fixed error if the nitrous use is not bound to any key

Fixes:
- Particles will no longer emit while the game is paused

Fixed NitrousEnabled being broken after recent update

Last one I swear