Review cancellation tokens

[askpt]

This review focuses on how cancellation tokens are implemented and handled within the Flagd provider. The main areas of attention include:

• Consistent and proper propagation of cancellation tokens through all asynchronous operations.
• Ensuring that cancellation tokens are not ignored or omitted, especially in public APIs and long-running tasks.
• Appropriate response to cancellation requests (e.g., promptly throwing OperationCanceledException where expected).
• Avoidance of unnecessary or redundant creation of new tokens instead of passing existing ones.
• Documentation and code comments that clarify the intended use of cancellation tokens in relevant methods.

Please verify that cancellation tokens are used effectively to support graceful shutdown and resource management, and that their usage follows .NET best practices.