feat: Support cancellation notification while request timeout

[CrazyHZM]

Motivation and Context

How Has This Been Tested?

Breaking Changes

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

[chemicL]

I am not sure we should send a cancellation notification for timeouts. Can you point me to the specification where it is mentioned timeouts should issue cancellation notifications? I agree cancellations should be supported, but I'm uncertain whether it should be automatically issued for timing out of requests.

[CrazyHZM]

@chemicL
The specification does not indicate that a requirement notification needs to be sent when the timeout occurs, but I think this is a reasonable scenario for canceling the request because the client no longer cares about the response. I think it should be proposed as a specification when handling timeouts.
I created an issue to discuss this matter: modelcontextprotocol/modelcontextprotocol#418

[chemicL]

@CrazyHZM thanks. I suggest we close the PR for now and feel free to reopen it if the issue for the spec update is resolved positively.