Fixed memory leak and enhance KupTheme support

[stefanolanari]

This pull request introduces improvements to event listener management in kup-box and adds enhanced support for Constructable StyleSheets in the kup-theme manager. The most significant changes focus on memory leak prevention for event listeners and optimizing theme/style management for web components that support adopted style sheets.

Event Listener Management Improvements:

• Refactored the way the clickFunction is bound and stored in kup-box by introducing a dedicated #boundClickFunction property, ensuring the same function reference is used for both adding and removing the event listener. This prevents potential memory leaks and ensures proper cleanup. [1] [2] [3]

Constructable StyleSheets and Theme Management Enhancements:

• Added detection for Constructable StyleSheet support and a set of target components (adoptedStyleSheetsTargets) in kup-theme, enabling more efficient and modern style management for supported browsers.
• Implemented caching and updating of shared stylesheets via the new sharedSheets map and the updateSharedSheets method, ensuring styles are efficiently reused and updated across components. [1] [2] [3]
• Refactored the setKupStyle method to use Constructable StyleSheets when possible, improving performance and encapsulation for supported components. The method now distinguishes between components that support adopted style sheets and those that do not, applying styles accordingly. [1] [2]
• Extracted and documented a new getSharedStyle helper to centralize the logic for combining global, theme, and component-specific styles. [1] [2]