No way to get `request_id` for a tool call to cancel it

[ihrpr]

Describe the bug
When trying to cancel a tool by sending a cancel notification, there is no way to know request_id.

It would be useful to set a request id during the tool call.

To Reproduce
Try cancelling a tool call

Expected behavior
Have a reques_id known to cancel it

[davemssavage]

As an alternative to having to expose the request id outside of the client session #628 uses the cancel scope that the session is running in to trigger cancelation, this feels more natural to me and hides the internal protocol details inside the client, I'm not sure request_id has any usage outside of cancelation, if there are other use cases then other approaches may be more appropriate.