test: add tests for config package

[adcondev]

🎯 What: Added missing unit tests for internal/config package, focusing on the Update method.
📊 Coverage: Covers all paths in Update (full updates, partial updates with empty strings, and no changes), plus coverage for Get, New, and GetEnvironment.
✨ Result: Reaches 100% statement coverage for internal/config/config.go.

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PR created automatically by Jules for task 15731251382076474140 started by @adcondev

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[github-actions]

⚡ Benchmark Results

⚠️ No benchmarks found in the current codebase.

To add benchmarks, create functions starting with Benchmark in *_test.go files.

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.

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