I got carried away with Gemini and basically rewrote CI and the release
process for the new LLM reality. This work was largely completed by
Gemini.
- Bump all SDK versions to the current beta (3.9.0-0)
- Run `flutter channel beta`
- Wrote `ci_script.dart` to replace the bash scripts
- Converted repository to pub workspace #2499
- Added llm.md and release.md
- Added redirect for deprecated Samples Index
## Pre-launch Checklist
- [x] I read the [Flutter Style Guide] _recently_, and have followed its
advice.
- [x] I signed the [CLA].
- [x] I read the [Contributors Guide].
- [x] I have added sample code updates to the [changelog].
- [x] I updated/added relevant documentation (doc comments with `///`).
* Upgrade to pkg:provider 4.0
* Follow best practice of ProxyProvider updating
The addresses feedback from https://github.com/flutter/samples/issues/245. Instead of constructing a new `CartModel`, we merely update the `catalog` field.
We no longer need a fancy constructor, and `CartModel._catalog` cannot be final any more.
