fix(Auth): Refactoring state machine logic to fix memory leak

[harsh62]

Description

The PR aims at fixing memory leaks that have come up in Auth plugin with the usage of Async Sequence.

Rootcause:

• Async stream is unable to notify state machine of early exits, which resulted in subscriber never getting removed and hence causing leaks.

Following are the changes that have been made.

• Using combine framework to use CurrentValueSubject instead of maintaining the subscriptions ourselves.

Integration Test:

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General Checklist

• Added new tests to cover change, if needed
• Build succeeds with all target using Swift Package Manager
• All unit tests pass
• All integration tests pass
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)
• Documentation update for the change if required
• PR title conforms to conventional commit style
• New or updated tests include Given When Then inline code documentation and are named accordingly testThing_condition_expectation()
• If breaking change, documentation/changelog update with migration instructions

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