feat: a repaired invalid span is shaded faintly, not solidly

src/render/renderer.cpp

@@ -1732,8 +1732,8 @@ void Renderer::draw_cursor_label(const Plot& plot, const PlotLayout& layout, con
 }
 
 void Renderer::draw_invalid_spans(const PlotLayout& layout) {
-  for (const Rect& band : layout.invalid_spans) {
-    if (band.w > 0.0f) fill_pixels(band, style_.invalid_fill);
+  for (const InvalidSpanLayout& band : layout.invalid_spans) {
+    fill_pixels(band.fill, band.repaired ? style_.invalid_repaired_fill : style_.invalid_fill);
   }
 }