Add a GULF client prototype

[gspencergoog]

Description

This creates a prototype of a simple parser for JSON streamed UI descriptions.

[gspencergoog]

/gemini summary

[gemini-code-assist]

Code Review

This pull request introduces a prototype for a simple GSP client, including the core library, an example application, and tests. The overall architecture is well-documented in the IMPLEMENTATION.md and the code is a good starting point.

My review focuses on improving maintainability and correctness. Key points include:

• Aligning the data model implementation with the design document by using code generation (freezed/json_serializable) to reduce boilerplate and prevent errors.
• Refactoring parts of the widget building logic to be more robust and less brittle to changes.
• Fixing a potential layout issue in the example application.
• Cleaning up test data to be more accurate.

Overall, this is a solid foundation for the new package. Addressing these points will make it more robust and easier to build upon.

[gemini-code-assist]

The TextField builder is wrapping the TextField widget with an Expanded widget. This forces the TextField to fill available space within a Flex widget (like Row or Column). While this works for the current sample JSON where it's inside a Row, it makes the builder less reusable. If a TextField component were used in a context without a Flex parent, it would cause a runtime layout error.

Widget builders in the registry should be self-contained and not make assumptions about their parent widgets. The Expanded widget should be part of the layout definition (e.g., as a separate Expanded component type) rather than being hardcoded into the TextField builder.

I suggest removing the Expanded widget from this builder.

Suggested change

	return Expanded(
	child: Padding(
	padding: const EdgeInsets.symmetric(horizontal: 8.0),
	child: TextField(
	decoration: InputDecoration(hintText: component.description),
	),
	),
	);
	return Padding(
	padding: const EdgeInsets.symmetric(horizontal: 8.0),
	child: TextField(
	decoration: InputDecoration(hintText: component.description),
	),
	);