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

首先使用 OpenJDK 24 重現 Firebase Admin Authentication 初始化，並檢查報告中提到的 Guava AbstractFuture$UnsafeAtomicHelper 相依性。確定是否可以透過 SDK 相依性解決該警告，還是需要提供相容性指引；完成的標準是已記錄受支援的設定，或警告不再出現。

由索引模型根據 Issue 內容生成。