Make sure currentUser is available upon startup

[Supereg]

Make sure currentUser is available upon startup

♻️ Current situation & Problem

We experience problems, where the Firebase currentUser was not directly available upon startup and therefore required busy-waiting approaches to make sure a firebase user is available on startup actions (e.g., see StanfordBDHG/PediatricAppleWatchStudy#83 (comment)).
Firebase v11.6.0 fixes this issue with firebase/firebase-ios-sdk#14141, making sure that the currentUser is available immediately. We raise the minimum required Firebase version to the latest one and updated our code comments.

⚙️ Release Notes

• Fixed an issue where the user account might not be available immediately.
• Raised minimum required Firebase SDK

📚 Documentation

Updated inline docs.

✅ Testing

Added UI test to verify that user account is available inside configure() if user is logged in.

📝 Code of Conduct & Contributing Guidelines

By submitting creating this pull request, you agree to follow our Code of Conduct and Contributing Guidelines:

• I agree to follow the Code of Conduct and Contributing Guidelines.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.70%. Comparing base (5dd57f9) to head (c6f3565).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #51      +/-   ##
==========================================
- Coverage   68.72%   68.70%   -0.02%     
==========================================
  Files          19       19              
  Lines        1202     1201       -1     
==========================================
- Hits          826      825       -1     
  Misses        376      376              

Files with missing lines	Coverage Δ
.../SpeziFirebaseAccount/FirebaseAccountService.swift	73.56% <100.00%> (-0.03%)	⬇️

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[PSchmiedmayer]

Thank you for all the updates & adding the automated tests; looks great!