GridStyle class abstract

Abstract base class for all grid styles.

Calculates common grid parameters once and delegates to paintGrid for style-specific rendering. This eliminates code duplication across grid styles.

Each grid style extends this class and implements paintGrid to render its specific pattern (lines, dots, crosses, etc.).

Example:

class MyGridStyle extends GridStyle {
  const MyGridStyle({this.customSize = 5.0});

  final double customSize;

  @override
  void paintGrid(
    Canvas canvas,
    NodeFlowTheme theme,
    ({double left, double top, double right, double bottom}) gridArea,
  ) {
    // Calculate style-specific positions and render
    final startX = (gridArea.left / theme.gridSize).floor() * theme.gridSize;
    // ... custom grid painting logic here
  }
}