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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[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

[powertools-for-aws-oss-automation]

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