feat: implement sunlight fading fix (PR #603)

Add user-toggleable setting to turn off display between refreshes,
which helps mitigate the sunlight fading issue on e-ink displays.

Changes:
- Add turnOffScreen parameter to HalDisplay methods
- Add fadingFix member and setFadingFix() to GfxRenderer
- Add fadingFix setting to CrossPointSettings with persistence
- Add "Sunlight Fading Fix" toggle in Display settings
- Update SDK submodule with turnOffScreen support

lib/GfxRenderer/GfxRenderer.cpp

@@ -531,7 +531,9 @@ void GfxRenderer::invertScreen() const {
   }
 }
 
-void GfxRenderer::displayBuffer(const HalDisplay::RefreshMode refreshMode) const { display.displayBuffer(refreshMode); }
+void GfxRenderer::displayBuffer(const HalDisplay::RefreshMode refreshMode) const {
+  display.displayBuffer(refreshMode, fadingFix);
+}
 
 std::string GfxRenderer::truncatedText(const int fontId, const char* text, const int maxWidth,
                                        const EpdFontFamily::Style style) const {
@@ -910,7 +912,7 @@ void GfxRenderer::copyGrayscaleLsbBuffers() const { display.copyGrayscaleLsbBuff
 
 void GfxRenderer::copyGrayscaleMsbBuffers() const { display.copyGrayscaleMsbBuffers(display.getFrameBuffer()); }
 
-void GfxRenderer::displayGrayBuffer() const { display.displayGrayBuffer(); }
+void GfxRenderer::displayGrayBuffer() const { display.displayGrayBuffer(fadingFix); }
 
 void GfxRenderer::freeBwBufferChunks() {
   for (auto& bwBufferChunk : bwBufferChunks) {

lib/GfxRenderer/GfxRenderer.h

@@ -37,6 +37,7 @@ class GfxRenderer {
   HalDisplay& display;
   RenderMode renderMode;
   Orientation orientation;
+  bool fadingFix = false;     // Sunlight fading fix - turn off screen after refresh
   int bezelCompensation = 0;  // Pixels to add for bezel defect compensation
   int bezelEdge = 0;          // Which physical edge (0=bottom, 1=top, 2=left, 3=right in portrait)
   uint8_t* bwBufferChunks[BW_BUFFER_NUM_CHUNKS] = {nullptr};
@@ -76,6 +77,9 @@ class GfxRenderer {
   void setOrientation(const Orientation o) { orientation = o; }
   Orientation getOrientation() const { return orientation; }
 
+  // Fading fix control
+  void setFadingFix(const bool enabled) { fadingFix = enabled; }
+
   // Screen ops
   int getScreenWidth() const;
   int getScreenHeight() const;