Maintenance: fix linting issues for `parser` package

[dreamorosi]

Summary

In #4549 we're introducing new and/or stricter linting rules. Because of this, we need to review existing code for the parser package and make sure it's passing the linting.

While working on it, we could also address some SonarCloud issues that have popped up over time.

Why is this needed?

See rationale in parent issue (#4549).

Which area does this relate to?

No response

Solution

No response

Acknowledgment

• This request meets Powertools for AWS Lambda (TypeScript) Tenets
• Should this be considered in other Powertools for AWS Lambda languages? i.e. Python, Java, and .NET

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[powertools-for-aws-oss-automation]

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