[Testing] Implement WAIT operation cancellation (optional)

[dhegberg]

Migration from aws/aws-durable-execution-sdk-python-testing#51

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Context

Add WAIT operation cancellation support

Technical Requirements

• Add WAIT operation cancellation support
• Implement timer cancellation when WAIT is cancelled
• Handle cancellation of already completed operations
• Add proper error handling for invalid cancellation requests
• Ensure execution continues properly after WAIT cancellation

Implementation Details

• File: src/aws_durable_execution_sdk_python_testing/checkpoint/processors/wait.py:75

Acceptance Criteria

• WAIT operation cancellation support added
• Timer cancellation implemented when WAIT is cancelled
• Cancellation of already completed operations handled
• Proper error handling added for invalid cancellation requests
• Execution continues properly after WAIT cancellation ensured

Note: This is marked as optional in the original document.