ESP32 Deep Sleep — Battery Saving (OLED + RTC RAM Counter)

The ESP32's Deep Sleep mode reduces current consumption to ~10 µA by shutting down the CPU and most peripherals, making it critical for battery-powered IoT devices. In this project, we use three different wake-up sources: a timer (15 seconds), an external pin (EXT0 — button GPIO 33), and touch (T0/GPIO 4). Variables marked with `RTC_DATA_ATTR` are preserved during deep sleep—the boot counter, timer wake counter, and button wake counter are continuously tracked. On each wake-up, the SSD1306 OLED