Added #

• Initial release of marker_widget.
• Off-screen renderer that converts any Widget into PNG bytes using:
  • RenderView + ViewConfiguration with logical & physical constraints.
  • RepaintBoundary and explicit PipelineOwner / BuildOwner lifecycle.
• MarkerIcon value object that encapsulates:
  • PNG bytes.
  • Logical size.
  • Device pixel ratio.
  • Conversion to BitmapDescriptor.bytes with MapBitmapScaling.
• MarkerIconRenderer:
  • Configurable default logical size.
  • Optional LRU-based in-memory cache with size limit.
  • Optional image-aware second pass via waitForImages.
• MarkerIconScalingMode:
  • logicalSize mode (stable logical size, default).
  • imagePixelRatio mode (pixel-perfect using imagePixelRatio).
• WidgetMarkerExtension.toMarkerBitmap:
  • Convert any widget into a BitmapDescriptor using the default (or injected) renderer.
  • Supports waitForImages, custom pixel ratio, bitmap scaling, and scaling mode.
• Top-level widgetToMarkerBitmap helper for use without a BuildContext.
• buildMarkerCacheKey helper for theme/locale/size-aware marker caching.
• Example app demonstrating:
  • Basic usage with a custom card-like marker.
  • Toggling between logical-size and image-pixel-ratio scaling modes.