Several fixes for the FirebaseAccountService

[Supereg]

Several fixes for the FirebaseAccountService

♻️ Current situation & Problem

This PR introduces several improvements for the FirebaseAccountService and fixes some bugs and issues.
We fixed an issue where the initial account would not be associated correctly and the following stateDidChange call would always be ignored independent if the state actually changed between the initial check and the call.
Further, we made minor changes to make sure that no user account is associated when we try to login or signup for a new user account. We previously always relied on the stateDidChange change handler to be called to complete operations like signup/signin/logout/delete. These operations now no longer rely on the stateDidChange listener to be called and instead always propagate their changes themselves.

⚙️ Release Notes

• Fixed an issue where the initial account wouldn't be associated properly and all future state changes would be ignored until logout.
• Handle existing user accounts on signIn and signUp request to be generally more robust against erroneous states.
• Do not always rely on the stateDidChange handler to be called.
• Added additional logging output.

📚 Documentation

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✅ Testing

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📝 Code of Conduct & Contributing Guidelines

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

[codecov]

Codecov Report

Attention: Patch coverage is 82.14286% with 35 lines in your changes missing coverage. Please review.

Project coverage is 66.76%. Comparing base (12e7b77) to head (271753b).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
.../SpeziFirebaseAccount/FirebaseAccountService.swift	82.15%	35 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #43      +/-   ##
==========================================
+ Coverage   66.61%   66.76%   +0.15%     
==========================================
  Files          19       19              
  Lines        1087     1176      +89     
==========================================
+ Hits          724      785      +61     
- Misses        363      391      +28     

Files with missing lines	Coverage Δ
.../SpeziFirestore/DocumentReference+AsyncAwait.swift	58.34% <ø> (ø)
.../SpeziFirebaseAccount/FirebaseAccountService.swift	71.09% <82.15%> (-0.34%)	⬇️

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[PSchmiedmayer]

Thank you for adding this @Supereg!