fix(auth): add protected data unavailable error

[harsh62]

Issue #

#3972

Description

We’ve been investigating and believe the root cause is related to iOS application lifecycle behavior—specifically prewarming and protected data access. When the app is launched in the background (e.g., after device reboot or during system prewarming), UserDefaults and Keychain data may be inaccessible because protected data is not yet available. Amplify attempts to read credentials during this phase, fails to find them, and interprets it as corruption—triggering an unexpected AuthError and wiping the credentials.

Apple Documentation: https://developer.apple.com/documentation/uikit/about-the-app-launch-sequence.

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.