fix: don't respond to cancelled requests

[DaleSeo]

Motivation and Context

This fixes the service loop so a locally produced response is not sent after the peer has already cancelled the matching request. The existing cancellation path removes the request id from local_ct_pool, so the response path now treats a missing id as the signal to suppress the late response instead of writing it to the transport. This keeps cancellation best-effort and race-safe while matching the MCP guidance that a receiver should not respond to a cancelled request.

How Has This Been Tested?

Add integration tests

Breaking Changes

None.

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