Relates to pygfx/wgpu-py#391

Using the async versions of the wgpu methods would possibly result in better performance, but also make pyscript support easier/possible (see pygfx/wgpu-py#407).

I think we already do all our wgpu calls from the animation function callback. So if we make that function async, and renderer.render() and probably flush(), that maybe it. Would need to look into this to be sure though.

For scripts that don't run an eventloop, we can offer a simple run utility (in wgpu or pygfx) that briefly runs an asyncio eventloop to make this animate-function run. Perhaps we can use a decorator to hide this stuff even more. Running the examples in our tests requires something similar.