feat(aci): Add ability to filter group open periods by event_id

[malwilley]

Closes ISWF-905

[linear]

ISWF-905 Implement filtering open periods by `eventId`

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[cursor]

Filtering sliced queryset causes TypeError at runtime

High Severity

When both per_page and eventId query parameters are provided, calling .filter(event_id=event_id_param) on the open_periods queryset will fail with a TypeError. The get_open_periods_for_group function returns group_open_periods[:limit], which slices the queryset when limit is not None. In Django, filtering a sliced queryset raises TypeError: Cannot filter a query once a slice has been taken. The test case only tests eventId without per_page, so this crash path is not covered.