Deprecation warnings with Java OpenJDK 24 - sun.misc.Unsafe usage in Firebase Admin SDK

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### [REQUIRED] Step 2: Describe your environment

* Operating System version: macOS Sequoia 15.5
* Firebase SDK version: 9.5.0
* Library version: 9.5.0
* Firebase Product: Firebase Admin
* Java version: OpenJDK 24

### [REQUIRED] Step 3: Describe the problem

Create a Java application using Firebase Admin Authentication
Use Java OpenJDK 24 as the runtime
Run the application
Observe deprecation warnings in the console output

What happened?
When running a Firebase Admin Authentication application with Java OpenJDK 24, the following deprecation warnings are displayed:
WARNING: A terminally deprecated method in sun.misc.Unsafe has been called
WARNING: sun.misc.Unsafe::objectFieldOffset has been called
WARNING: Please consider reporting this to the maintainers of class com.google.common.util.concurrent.AbstractFuture$UnsafeAtomicHelper
WARNING: sun.misc.Unsafe::objectFieldOffset will be removed in a future release
This appears to be related to the Firebase Admin SDK's dependency on Guava's AbstractFuture$UnsafeAtomicHelper class, which uses the deprecated sun.misc.Unsafe::objectFieldOffset method.
Expected behavior:
The Firebase Admin SDK should work without deprecation warnings on supported Java versions, or provide guidance on compatible Java versions.
Relevant Code:
java// Basic Firebase Admin initialization that triggers the warnings
FirebaseOptions options = FirebaseOptions.builder()
.setCredentials(GoogleCredentials.getApplicationDefault())
.build();

FirebaseApp.initializeApp(options);

// Any subsequent Firebase Admin operations will show the warnings
Additional context:

The warnings appear to be coming from the Guava library dependency used by Firebase Admin SDK
This may impact future compatibility when Java removes the deprecated sun.misc.Unsafe methods
The application functions correctly despite the warnings

まず、OpenJDK 24 で Firebase Admin Authentication の初期化を再現し、報告で名前が挙げられている Guava AbstractFuture$UnsafeAtomicHelper 依存関係を調査します。警告を SDK の依存関係によって解消できるのか、それとも互換性に関する案内が必要なのかを判断します。対応完了の条件は、サポート対象のセットアップが文書化されるか、警告が表示されなくなることです。

索引モデルが issue の本文から書いたものです。