ReactiveMapExtensions<K, V> extension

Extension methods on Map to create reactive maps.

These extensions allow regular Dart maps to be converted into reactive maps that automatically track changes and emit notifications when the map is modified.

Example usage:

// Create a reactive map
final userPrefs = {'theme': 'dark', 'fontSize': 14}.reactive;

// Listen for changes
userPrefs.stream.listen((snapshot) {
  print('Preferences changed!');
  print('Old: ${snapshot.oldValue}');
  print('New: ${snapshot.newValue}');
});

// Modify the map (triggers notification)
userPrefs.value['fontSize'] = 16;
userPrefs.value = Map.from(userPrefs.value); // Trigger notification