MessageElement class abstract

Abstract base class for message content elements.

This class implements the Strategy Pattern for message content rendering, allowing different types of content (text, images, files, etc.) to be displayed within messages while maintaining a consistent interface.

Each message element is responsible for:

• Converting itself to a displayable Widget
• Supporting immutable updates through copyWith
• Maintaining its own state and properties

Example implementation:

class TextElement extends MessageElement {
  final String text;

  TextElement(this.text);

  @override
  Widget toWidget(BuildContext context) {
    return Text(text);
  }

  @override
  MessageElement copyWith() => TextElement(text);
}