Fix: Add debouncing to theme updates to prevent CPU spike

[AryaXDG]

Summary

This PR fixes a critical performance issue where rapidly switching themes or using the color picker caused CPU usage to spike to 100% (Issue #3588).

Technical Details

The issue was caused by the extension triggering a full style recalculation and DOM repaint for every single input event. When a user rapidly clicked themes or dragged the color picker, ImprovedTube.myColors() and ImprovedTube.setTheme() were called dozens of times per second, overwhelming the browser's rendering engine.

Changes:

• Implemented a debounce mechanism in js&css/web-accessible/core.js for the storage-changed event listener.
• The theme update functions are now wrapped in a setTimeout (200ms).
• This ensures that heavy CSS injections only occur once the user has stopped their interaction, rather than on every intermediate step.

Fixes

Fixes #3588

[ImprovedTube]

thank you! @AryaXDG

would you also like to join us as a mentor for google summer of code if we are accepted?
(guiding a student with a project of 90 to 360 hours, some payment, option to travel there)

[AryaXDG]

Hey! @ImprovedTube
Thank you so much for this invitation!!! I would be honored to join the team as a Mentor for GSoC!

I am also looking forward to continuing my own active contributions to the project alongside guiding the students 😄

Here is my email for the official invite and next steps if we get accepted: aryadasgupta2004@gmail.com

Let's do this!