feat: cleanup activity construction code

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 87.50000% with 4 lines in your changes missing coverage. Please review.

Project coverage is 65.92%. Comparing base (072644b) to head (6f7ef2d).

Files	Patch %	Lines
yalexs/manager/activity.py	0.00%	3 Missing :warning:
yalexs/activity.py	95.83%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #136 +/- ## ========================================== - Coverage 65.97% 65.92% -0.05% ========================================== Files 31 31 Lines 2251 2248 -3 Branches 385 388 +3 ========================================== - Hits 1485 1482 -3 Misses 708 708 Partials 58 58 ```

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