Update colorist for Riverpod 3

[domesticmouse]

Pre-launch Checklist

• I read the Effective Dart: Style recently, and have followed its advice.
• I signed the CLA.
• I updated/added relevant documentation (doc comments with ///).
• All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-devrel channel on Discord.

[gemini-code-assist]

Code Review

This pull request updates the colorist codelab to support Riverpod 3. The changes primarily involve updating dependencies in pubspec.yaml files, regenerating provider files (.g.dart) with the new syntax, and updating the application code to use the new provider names.

The migration is mostly correct, but I've found a critical issue in two of the codelab steps (step_06 and step_07) where an incorrect import for flutter_riverpod/legacy.dart has been introduced. This will cause the build to fail for those steps. The import is not only incorrect but also unnecessary, as the required Ref type is already provided by the riverpod_annotation package. My review includes suggestions to remove these erroneous imports.

Other than this issue, the dependency updates and code modifications appear to be correct and consistent with the Riverpod 3 migration guide.

[domesticmouse]

Ahh, GenAI. The statement that the legacy imports are incorrect, is incorrect.

[domesticmouse]

The CI for this will turn green once #2348 lands and is merged into this PR