🧹 [code health improvement] Refactor extract_secrets to reduce nesting

[ffalcinelli]

🎯 What: Extracted the environment variable name generation and formatting logic from extract_secrets into a new, dedicated helper function format_env_var_name.

💡 Why: The extract_secrets function in src/utils/secrets/mod.rs had a deeply nested structure (>= 6 levels). The inline formatting logic with a multi-line closure for character mapping contributed significantly to this complexity. Extracting this logic into a helper function drastically flattens the loop body, improving readability and maintainability without altering the function's behavior.

✅ Verification: Ran cargo test and cargo test -p kcd --lib. All relevant unit tests, including test_extract_secrets, pass successfully. Code review confirmed the refactoring is safe and correct.

✨ Result: The extract_secrets function is now much easier to read and understand, and the codebase adheres better to the directive of avoiding deep nesting.

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PR created automatically by Jules for task 1189305483990298848 started by @ffalcinelli

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[codecov]

Codecov Report

❌ Patch coverage is 90.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 93.31%. Comparing base (88846ac) to head (fd46055).

Files with missing lines	Patch %	Lines
src/utils/secrets/mod.rs	90.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #120   +/-   ##
=======================================
  Coverage   93.31%   93.31%           
=======================================
  Files          33       33           
  Lines        2260     2260           
=======================================
  Hits         2109     2109           
  Misses        151      151           

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