Track file sizes

[jprochazk]

What

Fixes #2511

• Adds scripts/ci/sizes.py for measuring and comparing file sizes
  • This works for any files, not just WASM files
• Use the new script in a new reusable_track_size.yml workflow
  • Measures sizes of various files (.wasm, .js, demo .rrd), and uploads the results to GCS
  • Compares the results to main and posts a PR comment if the size changed significantly (+10% or -10%)
  • Builds file size graphs and pushes them to gh-pages on every commit to main
• Also updated the PR description template to include links to benchmark graphs and the new size graphs.

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)

• PR Build Summary
• Docs preview
• Examples preview

[github-actions]

Size changes

Name	Previous	Current	Change
Wasm	(none)	13.506 MB	+100%
JS	(none)	107.698 KB	+100%
arkit_scenes.rrd	(none)	41661.312 KB	+100%
detect_and_track_objects.rrd	(none)	59530.079 KB	+100%
dicom_mri.rrd	(none)	64877.033 KB	+100%
dna.rrd	(none)	781.257 KB	+100%
human_pose_tracking.rrd	(none)	56953.565 KB	+100%
plots.rrd	(none)	255.568 KB	+100%
structure_from_motion.rrd	(none)	7091.426 KB	+100%