Computed<T> class

A class that represents a derived value computed from one or more reactive sources.

The Computed class automatically tracks dependencies on Reactive instances and recalculates its value whenever any of its sources change. This enables creating a reactive dependency graph where changes propagate automatically.

Key features:

• Automatically updates when source values change
• Supports multiple reactive sources
• Provides both synchronous value access and reactive stream
• Supports middleware for customizing behavior
• Offers batch update control for optimizing multiple updates

Example usage:

// Create source reactive values
final firstName = Reactive('John');
final lastName = Reactive('Doe');

// Create a computed value that depends on both sources
final fullName = Computed([firstName, lastName], (sources) {
  return '${sources[0].value} ${sources[1].value}';
});

// Access the computed value
print(fullName.value); // "John Doe"

// When a source changes, the computed value updates automatically
firstName.value = 'Jane';
print(fullName.value); // "Jane Doe"

You can also attach middleware to a Computed instance to customize its behavior:

final formattedName = Computed([firstName, lastName], (sources) {
  return '${sources[0].value} ${sources[1].value}';
}, middlewares: [LoggingMiddleware<String>()]);