Fix doc build - run `cargo metadata` with `--offline` & `--no-deps`

[Wumpf]

What

• solves https://github.com/rerun-io/rerun/issues/8165 (don't close ticket yet, have to confirm that docs.rs actually works)

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

• PR Build Summary

• Recent benchmark results

• Wasm size tracking

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[teh-cmc]

Let's see how that goes before merging anything: https://github.com/rerun-io/rerun/actions/runs/11897219343

[Wumpf]

didn't go so well, we need another fix for this, doing this off main