Missing cast of by-period to date in summaries

[operdeck]

Prediction and ADM summaries did not always return the optional Period as the exact same date type, which causes problems with the new, stricter, polars

[codecov[bot]]

Codecov Report

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

Project coverage is 59.75%. Comparing base (fd4f94f) to head (1851188). Report is 2 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #245 +/- ## ======================================= Coverage 59.75% 59.75% ======================================= Files 29 29 Lines 3809 3809 ======================================= Hits 2276 2276 Misses 1533 1533 ```

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