Specta symbology override fix

[gjmooney]

Description

This fixes a bug where the first segment’s symbology override was not applied in a Specta presentation because the viewer panel rendered before the OpenLayers map had its layers, so the override was never applied.

Depends on #1130

Checklist

• PR has a descriptive title and content.
• PR description contains references to any issues the PR resolves, e.g. Resolves #XXX.
• PR has one of the labels: documentation, bug, enhancement, feature, maintenance
• Checks are passing.
  Failing lint checks can be resolved with:
  • pre-commit run --all-files
  • jlpm run lint
• If you wish to be cited for your contribution, CITATION.cff contains an author entry for yourself

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📚 Documentation preview: https://jupytergis--1134.org.readthedocs.build/en/1134/
💡 JupyterLite preview: https://jupytergis--1134.org.readthedocs.build/en/1134/lite
💡 Specta preview: https://jupytergis--1134.org.readthedocs.build/en/1134/lite/specta

[github-actions]

👈 Launch a Binder on branch gjmooney/jupytergis/sym-override-fix

[github-actions]

Integration tests report: appsharing.space