feat: add configurable sparkline baseline

[CharlVS]

Summary

• allow sparkline charts to accept a configurable baseline calculator with an initial-value default
• update the painter logic to classify segments against the chosen baseline and clamp drawing within range
• document the change in the package changelog and cover the helpers with tests

Testing

• flutter test packages/dragon_charts_flutter/test/sparkline_chart_test.dart (fails: Dart SDK 3.9.0 required but 3.8.1 is installed)

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https://chatgpt.com/codex/tasks/task_e_68f297f52dac8326a1202fb3dde565ac

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Note

Add a configurable baseline calculator to SparklineChart, refactor painter to classify against that baseline (clamped), and add tests plus changelog entry.

• Sparkline:
  • Configurable baseline: Introduce SparklineBaselineCalculator and SparklineBaselines (initialValue, average).
  • Update SparklineChart to accept baselineCalculator (defaults to initialValue).
  • Refactor painter to compute baseline, clamp within data range, and classify segments/colors and intersections against it.
• Tests:
  • Add unit tests for SparklineBaselines and widget test for custom baselineCalculator.
• Docs:
  • Update CHANGELOG.md to note the new sparkline baseline customization.

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[Copilot]

Pull Request Overview

This PR adds configurable baseline calculation for sparkline charts. Instead of using a fixed baseline (the average of all data points), sparkline charts can now accept a custom baseline calculator function, with the initial value as the new default.

Key Changes:

• Introduced SparklineBaselineCalculator typedef and SparklineBaselines helper class with initialValue (default) and average baseline calculation methods
• Updated SparklineChart and _CustomSparklinePainter to use the configurable baseline instead of the hardcoded average
• Added comprehensive test coverage for baseline calculators and custom baseline functionality

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
packages/dragon_charts_flutter/lib/src/sparkline/sparkline_chart.dart	Implements configurable baseline with typedef, helper class, and updated painter logic to use baseline instead of average
packages/dragon_charts_flutter/test/sparkline_chart_test.dart	Adds unit tests for baseline calculators and integration test for custom baseline parameter
packages/dragon_charts_flutter/CHANGELOG.md	Documents the new feature with default baseline behavior

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✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch codex/add-configurable-baseline-for-sparkline-charts

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[github-actions]

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