Optimize point clouds

[emilk]

In the nyud example, SceneSpatial::load_objects goes from 8.5ms to 16ms.

Classic:

Arrow:

TODO:

• [ ] Improve crates/re_query/benches/query_benchmark.rs with benchmarks of:
  • [x] full primary and full secondary
  • [ ] full primary and sparse secondary
  • [ ] full primary and splat secondary
  • [ ] full primary and missing secondary
• [ ] Realistic point cloud benchmark, similar to nyud and/or colmap, using actual Points3DPart::load
• [ ] Write tests for ComponentJoinedIterator:
  • [ ] full primary and full secondary
  • [ ] full primary and sparse secondary
  • [ ] full primary and splat secondary
  • [ ] full primary and missing secondary
• [ ] Optimize ComponentJoinedIterator:
  • Special case for the common case when the instance keys are identical (no need to compare them - if they are same length, and starts and end on the same key, with the length as the difference, then they are the same)

[emilk]

Some of this optimization work will be easier once we remove the "classic" store

[emilk]

Thanks to https://github.com/rerun-io/rerun/pull/1064 we are now down to 9 ms, which is within the noise of the classic store:

…but I still think we should spend a few hours making a benchmark and see if there are any low-hanging fruit in ComponentJoinedIterator

[emilk]

• Closing in favor of https://github.com/rerun-io/rerun/issues/1136