Incorrect handling of DST for regualar events

[freezingDaniel]

Checklist

• I can reproduce the bug with the latest version given here.
• I made sure that there are no existing issues - open or closed - to which I could contribute my information.
• I made sure that there are no existing discussions - open or closed - to which I could contribute my information.
• I have read the FAQs inside the app (Menu -> About -> FAQs) and my problem isn't listed.
• I have taken the time to fill in all the required details. I understand that the bug report will be dismissed otherwise.
• This issue contains only one bug.
• I have read and understood the contribution guidelines.

Affected app version

1.0.2

Affected Android/Custom ROM version

Android 13&14

Affected device model

Tab S6 Lite

How did you install the app?

F-Droid / IzzyOnDroid

Steps to reproduce the bug

1. Set Device TZ/clock to UTC+0
2. Set Device Date to 2024-03-25
3. Calendar settings: Events>Allow chaing event time zones
4. (untouched bug) Create regular event on 2024-03-30, 2024-03-31, 2024-04-01 at 5am with Timezone Berlin
5. (optional touched bug) Repeat 4. with 6am entries. Edit entries for 31&01 fixing the time that has shifted on its own
6. (optional) do the same in another app for e.g. 7am
7. Set Device Date to 2024-04-01

Expected behavior

Events should be saved correctly after first save even if saved accross DST seasons:

Actual behavior

The events that were only stored once are saved incorrectly
The double edited ones seem to be saved correctly, the first save stores the events incorrectly

Screenshots/Screen recordings

see above

Additional information

It has been a while since I originally encountered this issue (by missing an important appointment) but it was the reason I (unfortunately) had to stop using this Calendar.

While I have not verified this time, for my old issue I came to the conclusion:

• An event that's created while being in CET, is incorrectly stored and displayed once in CEST (ics file has incorrect DTSTART/DTEND time).
  This is very dangerous as it'll even show with the incorrect time in different apps, as the event itself is incorrectly stored.

Maybe related to: Issue-165

Potentially useful in case I missed something: SimpleMobileTools/Simple-Calendar#1973