feat(appcheck): Add consumable token verification support

[lahirumaramba]

This PR adds support for App Check token consumption (replay protection) to the app_check.verify_token() API

[gemini-code-assist[bot]]

Summary of Changes

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This pull request introduces a significant security enhancement to the Firebase Admin SDK's App Check functionality. It allows developers to enable replay protection for App Check tokens by providing a new consume option in the verify_token API. This ensures that tokens, once verified, can be marked as consumed on the backend, preventing malicious actors from reusing them in subsequent requests and bolstering the integrity of client-server interactions.

Highlights

• App Check Token Consumption: The app_check.verify_token() API now supports an optional consume parameter to enable replay protection for App Check tokens.
• HTTP Client Integration: An internal HTTP client (_http_client.JsonHttpClient) has been integrated into the _AppCheckService to facilitate communication with the App Check backend for token consumption.
• Replay Protection Logic: A new private method, _verify_replay_protection, was added to handle the API call to the App Check backend to check and consume tokens, returning an alreadyConsumed status.
• Claims Augmentation: When consume is set to True, the verified token claims will now include an already_consumed boolean field indicating if the token was previously used.

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[lahirumaramba]

@gemini-code-assist review

[lahirumaramba]

@gemini-code-assist review

[lahirumaramba]

@gemini-code-assist review