Allow calling EquiMq::run multiple times

[iiYese]

Miniquad & macroquad prefer global APIs. This allows apps to use APIs wherever they please & not have to worry about how their state is structured. The egui integration is an exception to this. While it still has a global interface you can only call it once. Effectively forcing you to funnel all of your state into a single point of control flow.

Running the ui multiple times should just give you access to the same context like the bevy integration already does.