Syncfusion Flutter UI Widgets

Invalid date

Enhancements:
- Added plot‑band customization support for Cartesian charts.
- Improved Calendar to show extended all‑day events more clearly with appointmentBuilder.

Bug Fixes & Stability Improvements:
- Updated all Flutter widgets to support Flutter SDK 3.35 and 3.38.
- Improved Signature Pad on Web; renderToContext2D now draws smoother, more accurate signatures.
- Fixed Gauge MarkerPointer image clipping.