Macropad hotkeys: Add screensaver mode to prevent OLED burn-in

[flavio-fernandes]

This commit introduces a screensaver mode to the Adafruit Macropad hotkeys script, addressing issue #2882.

Key Changes:

• Screensaver Activation: Added a new configurable parameter SCREENSAVER_START_TIME, which specifies the duration of inactivity (in seconds) before the screensaver activates.
• Class-Level Variables: Introduced class-level variables in the App class to track the last activity time, screensaver mode status, and breathing effect brightness.
• Screensaver Functions: Added helper functions:
  • enter_screensaver_mode(): Turns off the OLED display and LEDs, entering screensaver mode.
  • wake_from_screensaver(): Exits screensaver mode and restores the previous state of the display and LEDs.
  • screensaver_breathing_effect(): Implements a breathing LED effect during screensaver mode.
• Main Loop Integration: Modified the main loop to monitor inactivity and trigger the screensaver mode based on the specified timeout.

This update ensures the Macropad’s OLED display is protected from burn-in during extended periods of inactivity.

Fixes #2882.