Fix video backward seeking / stepping back sometimes getting stuck (in the presence of b-frames)

[Wumpf]

What

• Fixes https://github.com/rerun-io/rerun/issues/7956

Our PTS -> sample search algorithm wasn't quite right. Fixed this here and added a unit test. Unfortunately, I had to introduce a small auxiliary data structure to keep this snappy / not O(n) for n samples, but it's very simple and rather contained.

Tested on native & web. Web still suffers from

• https://github.com/rerun-io/rerun/issues/7961

but on Chrome this works fine now!

https://github.com/user-attachments/assets/7a20467d-4d66-456f-be99-debba4ff7a31

Checklist

• [x] I have read and agree to Contributor Guide and the Code of Conduct

• [x] I've included a screenshot or gif (if applicable)

• [x] I have tested the web demo (if applicable):

  • Using examples from latest main build: rerun.io/viewer
  • Using full set of examples from nightly build: rerun.io/viewer

• [x] The PR title and labels are set such as to maximize their usefulness for the next release's CHANGELOG

• [x] If applicable, add a new check to the release checklist!

• [x] If have noted any breaking changes to the log API in CHANGELOG.md and the migration guide

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[Wumpf]

known issue on error[unmaintained]:instantis unmaintained