chore(auth): Fix race conditions in read state machine states

[mattcreaser]

• PR title and description conform to Pull Request guidelines.

Issue #, if available:

Description of changes:

• Use onSubscription instead of onStart to trigger state machine events while collecting. onStart does not guarantee that emissions generated from the block are visible in downstream collectors when used on a SharedFlow.
• Use SharedFlow for emitting states instead of a StateFlow because StateFlow will conflate emitted values, which can skip required intermediate states in subscribers.

These changes shouldn't effect production behaviour, but in unit tests this resolves some race conditions that happened when states update too quickly.

How did you test these changes?

• Tests should pass

Documentation update required?

• No
• Yes (Please include a PR link for the documentation update)

General Checklist

• Added Unit Tests
• Added Integration Tests
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)
• Ensure commit message has the appropriate scope (e.g fix(storage): message, feat(auth): message, chore(all): message)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

❌ Patch coverage is 94.28571% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 54.25%. Comparing base (0440ba3) to head (39247a7).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3126      +/-   ##
==========================================
- Coverage   54.26%   54.25%   -0.01%     
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  Files        1040     1040              
  Lines       32062    32071       +9     
  Branches     4712     4712              
==========================================
+ Hits        17398    17400       +2     
- Misses      12826    12828       +2     
- Partials     1838     1843       +5     

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