feat(viz): implement RBF heatmap and custom QPainter trend chart item

Introduce Radial Basis Function interpolation for fine wafer thermal gradients and GraphQuickItem for high-performance trend line rendering.

src/pygui/backend/visualization/__init__.py

@@ -2,9 +2,10 @@
 from pygui.backend.visualization.graph_quick_item import GraphQuickItem
 from pygui.backend.visualization.graph_view import GraphView
 from pygui.backend.visualization.rbf_heatmap import interpolate_field
+from pygui.backend.visualization.trend_chart_item import TrendChartItem
 from pygui.backend.visualization.wafer_map_item import WaferMapItem
 
 __all__ = [
-    "GraphQuickItem", "GraphView", "WaferMapItem",
+    "GraphQuickItem", "GraphView", "TrendChartItem", "WaferMapItem",
     "interpolate_field",
 ]