`DreamObjectWorld` doesn't cope with conflicting `world.fps` and `world.tick_lag`

[ike709]

As of https://github.com/OpenDreamProject/OpenDream/pull/2019 we now handle tick_lag being set on the world object definition. However, we do not cope with tick_lag and fps having conflicting values. We just set one and then the other.

Ideally, we need to resolve conflicts between these vars at compile-time and then just read one of them at runtime.