Refactor power saving logic into display drivers and add ST7789 support

display/low_level_display_epaper.cpp

@@ -141,3 +141,24 @@ void LowLevelDisplayEPaper::sleep() {
     printf("Putting e-paper display to sleep...\n");
     EPD_4IN2_V2_Sleep();
 }
+
+void LowLevelDisplayEPaper::on_idle_2min() {
+    // E-paper doesn't dim
+}
+
+void LowLevelDisplayEPaper::on_idle_10min() {
+    if (!is_sleeping) {
+        sleep();
+        is_sleeping = true;
+        printf("E-Paper: Entered sleep mode\n");
+    }
+}
+
+void LowLevelDisplayEPaper::on_user_interaction() {
+    if (is_sleeping) {
+        printf("E-Paper: Waking from sleep...\n");
+        init(); // Re-initialize to wake up
+        is_sleeping = false;
+        printf("E-Paper: Ready\n");
+    }
+}