🧪 Add unit tests for UserOption Display implementation

[google-labs-jules]

🎯 What: The testing gap addressed is the lack of unit tests for the Display implementation of the UserOption struct in src/app/message.rs.

📊 Coverage:

• realname provided and non-empty.
• realname empty (should display only username).
• realname containing only whitespace (preserves existing behavior).
• username empty (edge case).
• Both username and realname empty.

✨ Result: The improvement in test coverage ensures the formatting logic for user options is verified and protected against regressions.

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PR created automatically by Jules for task 6314129216703630380 started by @jotuel

[google-labs-jules]

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