[Storage] [DataMovement] Setting delegate process to null and objects to null

[amnguye]

Part of attempt to resolve potential memory leak and encourage garbage clean up.

• Set Delegates to null at cleanup to let go of resources
• Set TransferManager to null after it becomes unnecessary to continue using
• Catch and log exception in the case that a process throws an error

Related to #51637

[Copilot]

Pull Request Overview

This PR addresses potential memory leaks in the Azure Storage DataMovement SDK by implementing proper resource cleanup and disposal patterns. The changes focus on nullifying delegate references and ensuring TransferManager instances are properly disposed.

Key changes:

• Set delegate process to null in ChannelProcessing cleanup to release references
• Set TransferManager reference to null in TransferInternalState after completion
• Updated all test classes to use await using pattern for TransferManager disposal

Reviewed Changes

Copilot reviewed 24 out of 24 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
TransferInternalState.cs	Nullifies TransferManager reference after transfer completion to release resources
ChannelProcessing.cs	Sets delegate process to null during cleanup to release references
DownloadChunkHandler.cs	Improves error handling with proper async/await pattern and logging
CommitChunkHandler.cs	Improves error handling with proper async/await pattern and logging
DataMovementEventSource.cs	Adds new event for logging unexpected transfer failures
Test files (multiple)	Updates all test classes to use await using for proper TransferManager disposal
Sample and documentation files	Updates examples to use await using pattern for TransferManager