Migrate to a Swift Charts wrapper for easier initialization

[andywkff]

Summary

Migrate SimpleChart to use a Swift Charts wrapper that makes initialization easier.

Context

This issue was created from the pasted SimpleChart roadmap under v2.0.

Acceptance Criteria

• The intended wrapper approach is defined.
• Chart initialization becomes simpler for the target use cases.
• The migration preserves the library's core charting capabilities.
• Any API changes or compatibility implications are documented.

[andywkff]

Verified on main: the package now ships a Swift Charts-first wrapper API (SCNative*, SCChartPoint, SCChartDomain) and the README plus CHANGELOG document the migration. Closing as completed.