use rtd theme 3 rc1

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (9b95437) to head (86c7ec7). Report is 2 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #624 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 34 34 Lines 532 532 Branches 29 29 ========================================= Hits 532 532 ```

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