Fix actor module documentation formatting

[tbillington]

Adds text section annotation to actor module docs to fix formatting in docs.rs

before

after

[codecov[bot]]

Codecov Report

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

Comparison is base (8c310e7) 79.73% compared to head (317ce7e) 79.73%. Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #198 +/- ## ======================================= Coverage 79.73% 79.73% ======================================= Files 50 50 Lines 9790 9790 ======================================= Hits 7806 7806 Misses 1984 1984 ```

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