Cleanup use of await/notify to recommended ReentrantLock/Condition and add nullness checking.

[scwhittle]

I thought there was an issue with nullness with the previous code after awaiting. However since we aren't removing from the cleanupQueue that can't occur. However we might as well clean this up to use better concurrency primitives than notify/await.

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Summary of Changes

Hello @scwhittle, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the concurrency management within the FinalizeBundleHandler by migrating from traditional await/notify mechanisms to modern ReentrantLock/Condition constructs. This change aims to improve the reliability and maintainability of the bundle finalization process, alongside introducing better nullness checking for increased code safety.

Highlights

• Concurrency Primitives Update: The FinalizeBundleHandler has been refactored to replace the use of Object.wait() and Object.notify() with the more robust java.util.concurrent.locks.ReentrantLock and java.util.concurrent.locks.Condition for managing concurrent access to the cleanup queue.
• Nullness Checking Improvements: The @SuppressWarnings("nullness") annotation has been removed, and @Nullable annotations have been added where appropriate, improving the code's null-safety and clarity regarding potential null values.
• Cleanup Logic Encapsulation: The core cleanup loop logic, previously inline within the FinalizeBundleHandler constructor, has been extracted into a dedicated private method cleanupThreadBody() for better organization and readability.

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[github-actions]

Checks are failing. Will not request review until checks are succeeding. If you'd like to override that behavior, comment assign set of reviewers

[scwhittle]

assign set of reviewers

[scwhittle]

failures appear unrelated

[scwhittle]

Run Java PreCommit

[github-actions]

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R: @ahmedabu98 for label java.

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