twenties: improve energy efficiency and simplify scheduling logic

[splch]

This PR refactors the buzzing functionality in the twenties app to enhance energy efficiency:

Key Improvements:

• Simplifies and consolidates the logic determining active work hours (Mon–Fri, 8 am–6 pm).
• Optimizes scheduling to avoid unnecessary checks outside working hours, significantly improving battery performance.
• Renames variables for clearer readability (isWorkTime, LOOP_INTERVAL, BUZZ_INTERVAL).

[bobrippling]

LGTM, thanks!