chore: Add return type for functions

[lym953]

What does this PR do?

Add explicit return type for functions.

Motivation

Most functions in the codebase don't have an explicit return type. Adding it would make code more readable, improving developer experience.

Testing Guidelines

npm test

Additional Notes

Types of Changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• This PR's description is comprehensive
• This PR contains breaking changes that are documented in the description
• This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• This PR impacts documentation, and it has been updated (or a ticket has been logged)
• This PR's changes are covered by the automated tests
• This PR collects user input/sensitive content into Datadog

[lym953]

/merge

[dd-devflow]

🚂 MergeQueue: pull request added to the queue

The median merge time in main is 4m.

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