refactor(no-release): refactor inline structs to reusable types

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This code change improves the organization and reusability of data structures in a GitLab API client library. Instead of defining user information and other nested data directly within larger structures (which creates repetitive, hard-to-maintain code), the developers extracted these into separate, reusable components.

Specifically, they created standalone structures for:

• Award emoji users (people who react with emojis)
• Issue board assignees (people assigned to work on tasks)
• Board list assignees
• Deployment-related data (information about code deployments)

This refactoring eliminates code duplication across multiple files and makes the codebase cleaner and easier to maintain. All the functionality remains exactly the same - it's purely an internal reorganization that makes the code more professional and easier to work with. The extensive test file changes simply update the test cases to use the new, cleaner structure names instead of the old inline definitions.

Closes #2137 (closed)