ci: add Codecov token

[codecov[bot]]

Codecov Report

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

Project coverage is 67.79%. Comparing base (2eb6095) to head (5c5ea18). Report is 10 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #324 +/- ## =========================================== - Coverage 99.27% 67.79% -31.48% =========================================== Files 24 37 +13 Lines 550 1177 +627 Branches 23 72 +49 =========================================== + Hits 546 798 +252 - Misses 2 376 +374 - Partials 2 3 +1 ```

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