events property

Structured event system for handling various editor events.

Events are organized into logical groups (node, connection, viewport, etc.) for better discoverability and maintainability.

Example:

NodeFlowEditor(
  controller: controller,
  nodeBuilder: nodeBuilder,
  theme: theme,
  events: NodeFlowEvents(
    node: NodeEvents(
      onTap: (node) => handleNodeTap(node),
      onDragStart: (node) => print('Dragging ${node.id}'),
    ),
    viewport: ViewportEvents(
      onCanvasTap: (pos) => clearSelection(),
    ),
    connection: ConnectionEvents(
      onBeforeComplete: (context) {
        // Validate connections
        return ConnectionValidationResult(allowed: true);
      },
    ),
    onInit: () => controller.fitToView(),
  ),
)