Add callback support and expanded Chart.js samples

[ipax77]

Summary

• Adds callback/function serialization support, binary dataset payloads, dataset update improvements, and TypeScript interop restructuring.
• Expands sample coverage for callbacks, scriptable options, plugins, legends, scales, tooltips, animations, gradients, and chart variants.
• Adds benchmark scaffolding plus broader serialization and Playwright coverage.
• Updates README, CI workflows, and project structure for the 0.9.0 preview work.

Validation

• dotnet build src\pax.BlazorChartJs\pax.BlazorChartJs.csproj passed with 0 warnings and 0 errors.

Notes

• Draft PR from callback into master.
• Branch compare before creation showed callback 64 commits ahead and 0 commits behind master.