Add more uniforms to .snapshot()

[Vipitis]

Also fixes #34 by keeping the fractional part.

by skipping the ._update() method for offscreen=True variant we can easily set most of the uniforms in the snapshot method. Should make this very close to deterministic.

note: whole offscreen and snapshot situation needs a rework, as there are recent improvements in wgpu-py that should make it easier. But will look into that at a later date, the current implementation will do.

[Vipitis]

looks like some other stuff broke too... will have a look later

[Vipitis]

little lost on the CI thing for screenshots here. it seems to not collect any tests ( 0 out of 1) for this workload... It should be 22 collected and 1 selected instead.
Which is the odd part to me. I saw multiple changes screenshot testing and CI for wgpu-py and tried to make a few of these changes - but not really getting it working right now.
I tried this on a remote linux machine and made sure it's using llvmpipe and it did pass and generate the screenshot just fine - so I am unsure what the differences to Github CI are (I didn't use the CI runner image).

remaining more things to try:

• example testutils as an actual module (but test examples works right now) ref: Fixes to testing wgpu-py#604
• difference in the workflow script between ci.yaml and screenshot.yaml: screenshots has an additional apt repository (but wgpu-py also has it):

In light of #31 and the potential to remake this whole thing in the future, I had hoped to find a small patch to make this

[Korijn]

You could try printing the full stdout & stderr of the subprocess in _determine_can_use_wgpu_lib to see if there's any clues there

[Vipitis]

so... it turns out it was this alternative drivers that caused a panic somehow (your review comment about it vanished). Which is why there are differences between the two workflows.

So wgpu-py removed this from ci.yaml in pygfx/wgpu-py#350 but never from the screenshots.yaml (it's still there) which is how we inherited it. And it must have became a problem recently.

will add the docs and this should be good