Added Biometric Authentication Support

[fhasse95]

This PR adds biometric authentication support to SkipKit. The extension allows for the checking of available biometric capabilities and displaying of the corresponding authentication prompt depending on the platform.

Check if biometric authentication is available:

if BiometricAuthentication.canAuthenticate {
    print("Biometric authentication is available")
}

Perform the biometric authentication:

BiometricAuthentication.authenticate(
    localizedReason: "Unlock the app"
) { result in
    // Handle the result.
}

For more information, check out the updated ReadMe file.

A complete example is also available in the BiometricAuthenticationPlayground of the Skip Showcase app:

Related PR:

• Added Biometric Authentication Playground skipapp-showcase#116

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• REQUIRED: I have signed the Contributor Agreement
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• AI was used to generate or assist with generating this PR. Please specify below how you used AI to help you, and what steps you have taken to manually verify the changes.

The initial implementation was generated with assistance from Codex. The resulting code was manually reviewed, refined where necessary, and validated using both the Skip Showcase app and my own app on iOS, iPadOS, macOS (Catalyst), and Android to ensure correctness and consistent cross-platform behavior.

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