refactor(tracer): fix code quality issues

[dwrth]

Summary

Changes

This PR fixes the code quality issues found by SonarCube mentioned in this ticket by refactoring the following:

Tracer.test.ts:

• Mark the memberVariable of Lambda as readonly
• Remove union type aliases on Subsegment instantiations

Tracer.ts:

• Remove redundant return statement in setCaptureHTTPsRequests
• Replace explicit return type from private method setOptions with this

Issue number: closes #4257

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[boring-cyborg]

Thanks a lot for your first contribution! Please check out our contributing guidelines and don't hesitate to ask whatever you need.
In the meantime, check out the #typescript channel on our Powertools for AWS Lambda Discord: Invite link

[dreamorosi]

Thank you for the PR, I left only one comment - after it's addressed I'll be happy to merge it!

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
20.0% Duplication on New Code

See analysis details on SonarQube Cloud

[dreamorosi]

Thank you for this PR and for helping making this project better!

We have a few other items similar to this in complexity and scope, if you're interested take a look here.

[boring-cyborg]

Awesome work, congrats on your first merged pull request and thank you for helping improve everyone's experience!