refactor: optimize async and await in code

[dev-itsheng]

Description

Optimized some async / await writing in the code:

1. If a function does not have await inside, then it does not need to prepend async.
2. If a function returns a Promise, add await in front to guarantee the execution order. Similarly, if a function returns a non-Promise value, it does not need to be preceded by await.

Additional context

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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• Read the Contributing Guidelines.
• Read the Pull Request Guidelines and follow the Commit Convention.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.

[bluwy]

Nice find!