fix(auth): Emit SIGNED_IN event after autoSignIn

[mattcreaser]

• PR title and description conform to Pull Request guidelines.

Issue #, if available: #3064

Description of changes:
Fixes two issues found in AutoSignInUseCase:

• The hub emitter was being called after emitting the sign in result. This doesn't work because of the use of the first() terminal operator, which cancels flow collection as soon as the sign in result is received. This would cancel the suspended coroutine and thus it never resumes to proceed to emitting the hub event.
• The use case was reusing the same hub emitter for multiple instances. This is the wrong pattern and would result in subsequent events potentially not being emitted if there were multiple sign ups within a single app session.

I also changed the transforming function from transformWhile to mapNotNull to make it more obvious that the collector is cancelled when the result is emitted.

How did you test these changes?

• Verified event is emitted using autoSignIn
• Added unit test to ensure event is emitted

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

Attention: Patch coverage is 57.14286% with 3 lines in your changes missing coverage. Please review.

Project coverage is 51.95%. Comparing base (04209f9) to head (ff49f6b).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3068      +/-   ##
==========================================
- Coverage   51.97%   51.95%   -0.02%     
==========================================
  Files        1032     1032              
  Lines       31329    31326       -3     
  Branches     4536     4536              
==========================================
- Hits        16282    16276       -6     
- Misses      13360    13362       +2     
- Partials     1687     1688       +1     

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[mattcreaser]

Codecov says coverage dropped but that appears to be an issue with Kover missing lines. That would maybe be fixed with a Kover version update as we are quite behind.