Improve render performance

[Zuzka-Cat]

I used Opus 5 to speedup the rendering as the slice and preview tab was sluggish on my high refresh monitor, with success. I don't know if ai code is wanted but it is an improvement. I also still feel some hitches sometimes when dragging around a model, i don't know if that was the case beforehand or not. I haven't tested if there are regressions, i suspect there could be on non fdm modes. I feel like i can work on it a bit more and let opus look how other slicers improve the performance. I also saw WebGL2 in the changes, i don't know if this K:M supposed to work with WebGL 1.0 then it would need further changes definitely.

Opus says:
I stopped Kiri from rebuilding every object's world matrix each frame, made layer materials shared and correctly opaque instead of per-slice and falsely transparent, merged each slice's geometry (and the whole ruler's per-glyph label meshes) into single draw calls, and added GPU occlusion culling that skips bands of layers proven hidden by a depth query.

Draw calls dropped from 120–539 to 8–41 and CPU time inside renderer.render fell from 3.3–5.6 ms to 0.16–0.56 ms — roughly 15–20×.

Measured in Firefox at 520 Hz: slice view went 201 → 355 fps and preview 207 → 353 fps on a 2.36 M-triangle model, while a solid 9.5 M-triangle model went 97 → 512 fps in slice view (occlusion culling drops it to 35 k triangles drawn, pixel-identical) — median frames now hit the 520 Hz cap, though dense previews while orbiting still sit around 108–318 fps.