Add animated keys

Add kes which are animated to shine etc.

The issue is about adding animated keys to a Kivy-based calculator UI. Look at the existing key widgets in the UI files to understand their structure. Research Kivy animations (like Animation or Clock schedules) to create a shining effect. Check if there are any existing styling or theming files to maintain consistency. The goal is to make keys visually dynamic without breaking the calculator's functionality.

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