fix(#173): throw 409 on user already exists

[h1alexbel]

closes #173

---

PR-Codex overview

This PR focuses on modifying the register_user function to return a tuple containing a StatusCode and an error message when a user registration fails, specifically returning a StatusCode::CONFLICT for existing users. Additionally, it introduces a new test case for this behavior.

Detailed summary

• Changed the return type of register_user from Result<StatusCode, String> to Result<StatusCode, (StatusCode, String)>.
• Updated the error handling to return StatusCode::CONFLICT when user registration fails due to an existing user.
• Added a new test case returns_409_when_user_exists to verify that a conflict status is returned when trying to register an existing user.

✨ Ask PR-Codex anything about this PR by commenting with /codex {your question}

[h1alexbel]

@rultor merge

[rultor]

@rultor merge

@h1alexbel OK, I'll try to merge now. You can check the progress of the merge here

[rultor]

@rultor merge

@h1alexbel Done! FYI, the full log is here (took me 15min)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.19%. Comparing base (22448a3) to head (3aeb8b9).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #185      +/-   ##
==========================================
+ Coverage   82.13%   82.19%   +0.06%     
==========================================
  Files          16       16              
  Lines         291      292       +1     
==========================================
+ Hits          239      240       +1     
  Misses         52       52              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[0crat]

@h1alexbel Great work on your contribution! 🌟 You've earned +4 points, bringing your total to +67. While there's room for improvement in code reviews and comments, we appreciate your effort. Keep the contributions coming – your progress is valuable to the team!