Fix brick_breaker

[domesticmouse]

Context:

~/work/codelabs/codelabs/brick_breaker/step_09 ~/work/codelabs/codelabs
== Testing
Analyzing step_09...

  error - lib/src/brick_breaker.dart:20:49 - Classes can only mix in mixins and classes. - mixin_of_non_class
  error - lib/src/brick_breaker.dart:104:11 - The method 'onTap' isn't defined in a superclass of 'BrickBreaker'. Try correcting the name to the name of an existing method, or defining a method named 'onTap' in a superclass. - undefined_super_member
warning - lib/src/brick_breaker.dart:103:8 - The method doesn't override an inherited method. Try updating this class to match the superclass, or removing the override annotation. - override_on_non_overriding_member

3 issues found.

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.

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[gemini-code-assist]

Code Review

This pull request primarily updates dependencies, including a new version of the Flame engine, and adapts the code to its API changes. It also adds build steps for multiple platforms to the codelab configuration. While the core changes are correct, I've identified significant code duplication in the YAML configuration that should be addressed to improve maintainability. I've also suggested minor improvements in the Dart code to align better with Effective Dart style and general best practices.