Auditing EventsService::Updater #90

A few updates from combing over the code that I hope will make operations more
understandable.
- Make it clear which attributes from events vs occurrences are being updated.
- Better understand test cases, like one that updates a recurring event to
 create a one-off event.
- Refactor rename_task_ids

- Bundle csv gem because it's no longer part of the std lib [1]
- Upgrade icalendar gem to remove ostruct warning [2]
- Use `it` for anonymous block parameter (standardrb requirement)
[1]: https://www.ruby-lang.org/en/news/2024/12/25/ruby-3-4-0-released/#standard-library-updates
[2]: https://github.com/icalendar/icalendar/blob/main/CHANGELOG.md#2103---2024年09月21日