docs: Add XML documentation to IEnvironmentVariables interface

[thomhurst]

Summary

• Adds comprehensive XML documentation to the IEnvironmentVariables interface
• Documents the interface purpose for reading and modifying environment variables
• Adds parameter and return documentation for all 5 methods

Fixes #1522

Test plan

• Build succeeds with no errors
• XML documentation is syntactically correct
• IntelliSense shows documentation when hovering over interface members

🤖 Generated with Claude Code

[thomhurst]

Summary

Adds comprehensive XML documentation to the IEnvironmentVariables interface, documenting all 5 methods with parameter descriptions and return values.

Critical Issues

None found ✅

Verdict

✅ APPROVE - No critical issues

The documentation is accurate, follows the existing codebase patterns (consistent with other interfaces like IBase64), and correctly describes the implementation behavior. All methods, parameters, and return values are properly documented with clear, helpful descriptions.

[Copilot]

Pull request overview

This PR adds comprehensive XML documentation to the IEnvironmentVariables interface to improve IntelliSense support and developer experience. The documentation describes the interface's purpose for managing environment variables and includes detailed parameter and return value documentation for all five methods.

Key Changes:

• Added interface-level summary explaining environment variable management functionality
• Documented all method parameters with clear descriptions including default values and behavior
• Added return value documentation with null-handling details where applicable