Fix #5331: update system-wide alert preview countdown dynamically

[guillermo-escire]

References

Fixes #5331

Description

Fixes the system-wide alert countdown timer in the preview. The countdown now updates dynamically every second and disappears when it reaches zero.

Instructions for Reviewers

Changes included in this PR:

• Added checks for date and time before updating the preview to prevent errors.
• Modified the allocateTimeUnits function so that when the countdown reaches zero, days, hours, and minutes are set to 0 and the visible countdown stops.
• Adjusted the previewSubscription using interval(1000) to refresh the countdown every second.
• Added a comment to the previewSubscription variable for consistency with other variables (counterEnabled$, previewMinutes, previewHours, previewDays).

How to test:

1. Go to System Alerts → System-Wide Alert.
2. Activate an alert and enable the countdown timer.
3. Set the timer to one minute in the future.
4. Observe the alert preview: the countdown should update dynamically every second showing the correct remaining time.
5. When it reaches zero, the counter disappears from the banner.

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[kanasznagyzoltan]

@guillermo-escire
I have tried for me when you see in my video that "In 1 minute" disappeared i had to click on somewhere and the preview is automatically updated. What did I do wrong?

pr_5383_converted.mp4

[nathanmlf]

@guillermo-escire
I've been testing it locally and it seems to not be working quite as expected on my side. I am not sure if I am missing a step, but when the timer drops below 1 minute, the countdown disappears completely from the preview banner instead of showing the remaining seconds.

I noticed @kanasznagyzoltan might have run into the exact same issue based on the video uploaded above. I've also attached a quick video below showing the behavior on my end.

Observation: I posted it as "Suggested change" but it's essencially a commentary, thanks for the hark work!

pr_5383.mp4