Docs: retry ui-bundle downloads

[sdarwin]

Any download during a CI build might potentially fail so it's convenient to retry. This PR includes a new extension "@cppalliance/antora-downloads-extension" with a retry loop for the ui-bundle.

[cppalliance-bot]

An automated preview of the documentation is available at https://944.url.prtest2.cppalliance.org/index.html

If more commits are pushed to the pull request, the docs will rebuild at the same URL.

2025-11-13 05:21:05 UTC

[cppalliance-bot]

GCOVR code coverage report https://944.url.prtest2.cppalliance.org/gcovr/index.html
LCOV code coverage report https://944.url.prtest2.cppalliance.org/genhtml/index.html
Coverage Diff https://944.url.prtest2.cppalliance.org/gcovr/coverage_diff.txt

Build time: 2025-11-13 05:31:36 UTC

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.21%. Comparing base (bbe9700) to head (da6edae).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #944   +/-   ##
========================================
  Coverage    99.21%   99.21%           
========================================
  Files          159      159           
  Lines         8684     8684           
========================================
  Hits          8616     8616           
  Misses          68       68           

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