Detect Pyodide to avoid get_asyncgen_hooks

[almarklein]

This should avoid the problems with sys.get_asyncgen_hooks() that @Vipitis encountered when trying to port to Pyodide.

[Vipitis]

I have to try this later. It's rather similar to the change I already made to _async.py in #753 (which is needed even with rendercanvas 2.4, since the logic to return None doesn't seem to work).

I don't expect this will solve the hang, as using rendercanvas 2.5 and calling any async function with pyodides sync_wait causes the hang if I recall correctly. Meaning it's not related to wgpu.

[almarklein]

Meaning it's not related to wgpu.

That makes sense; I am about to apply a similar change in rendercanvas.

[almarklein]

pygfx/rendercanvas#179

[almarklein]

@Vipitis you mentioned that the changes to _async.py in #753 work. However, I prefer the explicit approach in the current PR, otherwise we'd select 'asyncio' also when asyncio does not have a running loop.

@Korijn ready 🚀

[Vipitis]

sure, I will merge this variant into the PR branch as soon as I find time