refactor(metrics): replace EnvironmentVariablesService with cached #envConfig

[uttam282005]

• Removed EnvironmentVariablesService class.
• Replaced repeated environment variable reads with a single #envConfig object populated once during setOptions().
• Updated Metrics.ts to use #envConfig for values like namespace, serviceName, functionName, etc.
• Removed all references to envVarsService, including getEnvVarsService() and setEnvVarsService() methods.

This refactor improves runtime performance by avoiding redundant environment variable reads and follows a cleaner, more functional approach. It also aligns with the setOptions() pattern for centralized config management and eliminates ~50 lines of unnecessary code.

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Summary

What’s being changed?

This PR removes the verbose class-based EnvironmentVariablesService and replaces it with a private, cached #envConfig object in the Metrics class. The object is populated once during initialization via the setOptions() method using functional utilities from @aws-lambda-powertools/commons/utils/env.

Why?

• Performance: Avoids repeated environment variable lookups at runtime.
• Code quality: Cleaner, more maintainable, and aligns with existing config patterns.
• Consistency: Follows the tenets of making things explicit, safe, and minimal.

Benefits

• Improved runtime efficiency.
• Simplified implementation.
• Easier to reason about and maintain.

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#4136

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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

[uttam282005]

@svozza you are right. It's not actually needed as inferred type of the whole expression is string | undefined which is compatible with the type of namespace.
I will remove it.

[dreamorosi]

No acknowledgement section found. Please make sure you used the template to open a PR and didn't remove the acknowledgment section. Check the template at .github/PULL_REQUEST_TEMPLATE.md#acknowledgment

Hi @uttam282005 thank you for your contribution - please make sure to review the acknowledgment section here and paste it in the PR body as-is and without modifications if you agree with its text.

We won't be able to merge the PR otherwise. Thank you!

[dreamorosi]

Thanks for the PR!

A couple small changes to maintain full parsing of POWERTOOLS_METRICS_DISABLED and remove non-null assertions from the #envConfig.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

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

See analysis details on SonarQube Cloud

[uttam282005]

@dreamorosi I’ve implemented the suggested changes. Please let me know if there’s anything else that needs to be addressed.

[boring-cyborg]

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

[github-actions]

@aws-powertools/lambda-typescript No related issues found. Please ensure 'pending-release' label is applied before releasing.