Add an option to disable netvars

[Jovvik]

P vac bypass

Doesn't disable setting netvars entirely because rage sets angles and I cba to think of a way to restrict access to struct fields.

[hellidox]

what does this do, not set netvars but directly change memory relating to it?

[Jovvik]

directly change memory relating to it?

That's how netvars are changed in general. This PR just disables setting them and breaks any features that require writing to netvars.

[kehrazy]

@Jovvik use std::call_once pls ty