fix: dispose the text the charts lay out

A laid-out TextPainter holds a native paragraph and has to be disposed.
None of them were, and a chart lays out a few dozen labels a frame: over
eight thousand painters were left to the garbage collector across the test
suite alone.

TextPainterCache now disposes the painter it evicts, the ones clear()
drops and everything it still holds when the new dispose() is called; all
39 charts that own a cache dispose it with their state. The depth chart
was laying out every label afresh on every paint and throwing the painters
away — it goes through a cache like every other chart. The painters that
cannot be cached, because the cache keys on a plain string — a multi-span
legend row, an axis label, a marker label, an event glyph in its own icon
font — are disposed as soon as they are painted.

KChartWidget also disposes the CurvedAnimation wrapping each scroll
animation, rather than leaving one behind per fling.

The suite runs under leak_tracker from here on, so a widget that leaves a
disposable behind fails its file. The two ChangeNotifiers the caller owns,
ChartDrawingController and KChartController, are left out of it: the chart
attaches and detaches but never disposes what it did not make.

Author: CtrlAltDevelop

lib/src/book/book_heatmap_chart.dart

@@ -455,6 +455,13 @@ class BookHeatmapChart extends StatefulWidget {
 
 class _BookHeatmapChartState extends State<BookHeatmapChart> {
   final TextPainterCache _text = TextPainterCache(capacity: 64);
+
+  @override
+  void dispose() {
+    _text.dispose();
+    super.dispose();
+  }
+
   BookHeatmapLayout _layout = BookHeatmapLayout.empty;
   Offset? _pointer;
 

lib/src/bubble/bubble_chart.dart

@@ -397,6 +397,7 @@ class _BubbleChartState extends State<BubbleChart>
 
   @override
   void dispose() {
+    _text.dispose();
     _animation.dispose();
     super.dispose();
   }

lib/src/bullet/bullet_chart.dart

@@ -405,6 +405,7 @@ class _BulletChartState extends State<BulletChart>
 
   @override
   void dispose() {
+    _text.dispose();
     _animation.dispose();
     super.dispose();
   }

lib/src/calendar/calendar_chart.dart

@@ -545,6 +545,7 @@ class _CalendarChartState extends State<CalendarChart>
 
   @override
   void dispose() {
+    _text.dispose();
     _animation.dispose();
     super.dispose();
   }

lib/src/chord/chord_chart.dart

@@ -537,6 +537,7 @@ class _ChordChartState extends State<ChordChart>
 
   @override
   void dispose() {
+    _text.dispose();
     _animation.dispose();
     super.dispose();
   }

lib/src/delta/cumulative_delta_chart.dart

@@ -503,6 +503,7 @@ class _CumulativeDeltaChartState extends State<CumulativeDeltaChart>
 
   @override
   void dispose() {
+    _text.dispose();
     _animation.dispose();
     super.dispose();
   }

lib/src/depth_chart.dart

@@ -6,6 +6,7 @@ import 'depth_ratio_bar.dart';
 import 'depth_style.dart';
 import 'depth_translations.dart';
 import 'entity/depth_entity.dart';
+import 'renderer/text_painter_cache.dart';
 import 'renderer/depth_painter.dart';
 
 /// A market-depth chart for one order book.
@@ -102,9 +103,16 @@ class DepthChart extends StatefulWidget {
 }
 
 class _DepthChartState extends State<DepthChart> {
+  final TextPainterCache _text = TextPainterCache(capacity: 64);
   Offset? pressOffset;
   bool isLongPress = false;
 
+  @override
+  void dispose() {
+    _text.dispose();
+    super.dispose();
+  }
+
   @override
   Widget build(BuildContext context) {
     if (widget.mode == DepthChartMode.ladder) {
@@ -151,6 +159,7 @@ class _DepthChartState extends State<DepthChart> {
           widget.chartStyle,
           widget.offset,
           widget.chartTranslations,
+          textCache: _text,
           mode: widget.mode,
           scale: widget.scale,
           zoom: widget.zoom,

lib/src/distribution/box_plot_chart.dart

@@ -490,6 +490,7 @@ class _BoxPlotChartState extends State<BoxPlotChart>
 
   @override
   void dispose() {
+    _text.dispose();
     _animation.dispose();
     super.dispose();
   }

lib/src/distribution/histogram_chart.dart

@@ -367,6 +367,7 @@ class _HistogramChartState extends State<HistogramChart>
 
   @override
   void dispose() {
+    _text.dispose();
     _animation.dispose();
     super.dispose();
   }

lib/src/dumbbell/dumbbell_chart.dart

@@ -426,6 +426,7 @@ class _DumbbellChartState extends State<DumbbellChart>
 
   @override
   void dispose() {
+    _text.dispose();
     _animation.dispose();
     super.dispose();
   }