Optimize point cloud rendering

[emilk]

What

Makes open_photogrammetry_format example ~30% faster by only calling iter_required_component::<Point3D>() once per frame instead of twice.

Before: 158 ms/frame:

After: 119 ms/frame:

(debug builds)

This is a bit of a stop-gap until #2523 is fixed

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
• I've included a screenshot or gif (if applicable)
• I have tested demo.rerun.io (if applicable)

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[Wumpf]

a bit worrisome that reading from the store is that slow. Feels a bit more like a workaround for store reads that shouldn't be that slow?

[emilk]

Yeah, it is pretty crazy that it is this slow

[emilk]

I added a reminder in #2523 to revert this when we have optimized the store

[emilk]

Let's hold off merging this until we take a proper stab at #2523 - iterating through a bunch Vec3D in the store should be a almost zero-cost thing. The data should already be laid out exactly like a &[f32; 3]

[Wumpf]

Let's give it another spin on top of #2970

[emilk]

Will do

[emilk]

Latest main:

This PR with latest main merged in:

no difference. Let's close this PR!