docs: refactor sequential agent example - clean imports and test code

[adityamulik]

Refactored the code to use the imports in the example as it would become an easier copy paste for newcomers to try the multi-workflow agent without refactoring imports or making changes. Commented the rest of the code by adding comments for local testing for the maintainers of this repository.

Please let me know if theres any feedback or if this change is not needed.

[koverholt]

Thanks for the PR and for your contribution! I updated the Gemini model to 2.5 Flash per @joefernandez's comment, and I did some additional overdue cleanup on this script. Thanks for the fixes and making the example self-contained and easier for readers to run!