chore(auth): Move FetchAuthSession to usecase

[mattcreaser]

• PR title and description conform to Pull Request guidelines.

Issue #, if available:

Description of changes:

• Refactors the fetchAuthSession logic from callback code to coroutine-based usecase
• Adds additional code coverage for this logic
• Removes the now-unused KotlinAuthFacadeInternal class

How did you test these changes?
(Please add a line here how the changes were tested)

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 94.91525% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 55.80%. Comparing base (c9b0f0f) to head (7484325).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3246      +/-   ##
==========================================
+ Coverage   55.63%   55.80%   +0.17%     
==========================================
  Files        1079     1078       -1     
  Lines       31858    31825      -33     
  Branches     4751     4747       -4     
==========================================
+ Hits        17725    17761      +36     
+ Misses      12279    12222      -57     
+ Partials     1854     1842      -12     

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