🧪 [testing improvement] Add comprehensive tests for FromOptionString

[ffalcinelli]

🎯 What: The FromOptionString trait inside src/models.rs had missing and incomplete unit tests. The existing tests only partially verified its functionality combined with ToOptionString. We needed tests to clearly isolate and verify that set_from_option_string works correctly on both String and Option<String>.

📊 Coverage: The tests now explicitly cover setting String and Option<String> fields with both Some and None values, including updating an initially None option string to a Some value.

✨ Result: Test coverage for src/models.rs is expanded, ensuring any future changes to how strings are populated from options are securely tested against regressions.

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PR created automatically by Jules for task 3340030841962715910 started by @ffalcinelli

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.11%. Comparing base (983cd91) to head (20c7708).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #159   +/-   ##
=======================================
  Coverage   92.11%   92.11%           
=======================================
  Files          29       29           
  Lines        2358     2358           
=======================================
  Hits         2172     2172           
  Misses        186      186           

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