Updated blender_imgui.py to support global framerate max cap

[ItsCubeTime]

Hi @eliemichel !

I Updated the blender_imgui.py to support global framerate max cap, essentially what Im doing is checking if floor(timeSinceEpoch/framerate) is the same as it was last time that draw was called, if it is then we know that enough time hasnt passed to make it worthwhile to do another render.

The motivation was that sometimes the draw function gets called faster than whats seemingly necessary (it gets drawn faster than the modal function in a modal operator), stealing computation time from other tasks, as the overlays probably dont need to be called 120 frames per second it makes quite a lot of sense to me to try and limit it

[ItsCubeTime]

Not related to the PR, but as you put quite a lot of effort into making this library I figured it might feel satisfactory for you to see it actually being used somewhere https://github.com/ItsCubeTime/FastPBR/releases/tag/1.6.0 (this isnt my latest release but it has a video linked in the description showing what I currently use it for)