[Auth]: Add auth state stream utility

[nidegen]

Hi there!

Not sure if API extensions are also not allowed, but I figured this little helper could be useful to add some concurrency in Auth.

The struct AuthState is only there to avoid concurrency issues that appear when using a tuple instead.

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[nidegen]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces a utility for observing authentication state changes using Swift's AsyncStream. The AuthState struct and the authStateChanges property provide a convenient way to handle authentication events asynchronously. Overall, the changes seem well-structured and address the stated goal of adding concurrency to Auth.

Summary of Findings

• Naming consistency: Consider renaming AuthStateChanges to authStateChangesStream to clearly indicate that it is a stream of AuthState objects.
• Open access modifier: The open access modifier is used for both the AuthState struct and the authStateChanges property. While this allows for subclassing and overriding, it might be more appropriate to use public if external modification is not intended.

Merge Readiness

The changes introduce a useful utility for observing authentication state changes asynchronously. While the code appears functional, addressing the naming consistency and access modifier considerations would further improve its clarity and maintainability. I am unable to approve this pull request, and recommend that others review and approve this code before merging. I recommend that the author address the comments before merging.

[gemini-code-assist]

Consider renaming this property to authStateChangesStream to clearly indicate that it is a stream of AuthState objects. This would improve readability and make the intent more explicit.

Suggested change

	open var authStateChanges: AsyncStream<AuthState> {
	return AsyncStream { continuation in
	let listener = self.addStateDidChangeListener { auth, user in
	continuation.yield(AuthState(auth: auth, user: user))
	}
	continuation.onTermination = { _ in
	self.removeStateDidChangeListener(listener)
	}
	}
	}
	open var authStateChangesStream: AsyncStream<AuthState> {
	return AsyncStream { continuation in
	let listener = self.addStateDidChangeListener { auth, user in
	continuation.yield(AuthState(auth: auth, user: user))
	}
	continuation.onTermination = { _ in
	self.removeStateDidChangeListener(listener)
	}
	}
	}

[ncooke3]

Thanks for the PR, @nidegen! Are there use cases where you were intending to use the stream API? As a 1:1 replacement for the callback listener or perhaps in SwiftUI views?

[nidegen]

Just as a 1:1 replacement for the callback listener initially but definitely with SwiftUI tasks in mind:)

Not a big pain point, but I thought it might be welcome!