MultiSelectController<T> class

Controller for managing ControlledMultiSelect state programmatically.

Extends SelectController to provide reactive state management for multi-selection components. Manages a collection of selected items with methods for adding, removing, and bulk operations.

Example:

final controller = MultiSelectController<String>(['apple', 'banana']);

// Listen to changes
controller.addListener(() {
  print('Selection changed to: ${controller.value}');
});

// Update selection
controller.value = ['apple', 'cherry'];