Avoid recreating windows when only duration changes

[bbb651]

Description

Avoid recreating windows when only duration changes, and instead only updates the window close timer.
This avoids possible flicker with windows such as OSDs. The logic to do this was added in #263 but broke when durations were added.
Fixes #260.

Usage

N/A

Showcase

N/A, but here's my OSD that was flickering (WIP, haven't figured out the scss to remove the margin above the progress):

Additional Notes

N/A

Checklist

Please make sure you can check all the boxes that apply to this PR.

• All widgets I've added are correctly documented. (N/A)
• I added my changes to CHANGELOG.md, if appropriate. (N/A)
• The documentation in the docs/content/main directory has been adjusted to reflect my changes. (N/A)
• I used cargo fmt to automatically format all code before committing