Optimizations in Chart control

[PaulAndersonS]

Summary

This PR consolidates 10 performance improvements across the Chart control to reduce memory allocations, eliminate redundant LINQ evaluations, and improve CPU efficiency in hot rendering and interaction paths.

Performance Improvements

#	Fix	File(s)	Impact
1	Replace string-based double comparison with Math.Abs epsilon check	ChartDataUtils.cs	Critical - Eliminates 2 string allocations per call
2	Add direct type checks in ConvertToDouble to avoid redundant ToString()	ChartUtils.cs	High - Skips string conversion for numeric types
3	Materialize OfType<CartesianSeries>() to prevent repeated LINQ evaluation	CartesianChartArea.cs	High - Eliminates redundant type-check filtering
4	Remove unnecessary .ToList() on Dictionary.Values	CartesianChartArea.cs	Medium - Eliminates collection copy
5	Eliminate list copy in DataPointSelectionBehavior.ResetMultiSelection	DataPointSelectionBehavior.cs	High - Removes allocation in interaction path
6	Eliminate list copy in SeriesSelectionBehavior.ResetMultiSelection	SeriesSelectionBehavior.cs	High - Removes allocation in interaction path
7	Use HashSet for O(1) lookups in trackball point filtering	ChartTrackballBehavior.cs	High - O(1) vs O(n) Contains
8	Replace Cast<T>() LINQ wrapper with direct iteration	CircularSeries, FinancialSeriesBase, StepAreaSeries, AreaSeries, ScatterSeries, RangeAreaSeries	High - Eliminates LINQ enumerator overhead in rendering loops
9	Remove unnecessary .ToList() materialization	CartesianSeries.cs	Medium - Avoids intermediate collection
10	Replace separate Min()/Max() LINQ calls with single-pass loop	BoxAndWhiskerSeries.cs	Medium - O(n) instead of O(2n)

Build Verification

• ✅ dotnet build passes with 0 errors

[SaiyathAliFathima]

Fine