feat: cognito asf for react native

[pranavosu]

Description of changes

Adds Native Advanced Security Features (ASF) Context Data Support for React Native. This enables device fingerprinting data collection for Cognito's risk-based authentication on iOS and Android.

Changes:

• New @aws-amplify/rtn-asf package with TurboModule implementation for iOS (Swift) and Android (Kotlin)
• iOS native module using AWSCognitoIdentityProviderASF SDK
• Android native module using aws-android-sdk-cognitoidentityprovider-asf SDK
• Module loader in @aws-amplify/react-native with graceful degradation (returns undefined when not installed)
• Updated getUserContextData.native.ts in @aws-amplify/auth to use the native module
• UserContextData automatically included in signIn, signUp, and forgotPassword flows when available
• README documentation with installation steps for bare React Native and Expo

Behavior:

• When @aws-amplify/rtn-asf is installed: device context data is collected and sent to Cognito during auth flows
• When not installed: auth flows continue normally without context data (graceful degradation)

Issue #, if available

Resolves false detections for legitimate React Native mobile users when Cognito Advanced Security Features are enabled.

Description of how you validated changes

• Unit tests for module loader (loadAmplifyRtnAsf)
• Unit tests for getUserContextData.native.ts
• Property-based tests validating graceful degradation and output format transformation
• iOS native unit tests (AmplifyRtnAsfTests.swift)
• Android native unit tests (AmplifyRtnAsfModuleTest.kt)
• Integration tests verifying UserContextData inclusion in auth flows

Checklist

• PR description included
• yarn test passes
• Unit Tests are changed or added
• Relevant documentation is changed or added (and PR referenced)

Checklist for repo maintainers

• Verify E2E tests for existing workflows are working as expected or add E2E tests for newly added workflows
• New source file paths included in this PR have been added to CODEOWNERS, if appropriate

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