Investigate if we may need to dispose of the cancellation callback registeration

Within the invocation request method (`GrpcWorkerChannel.cs`) we register a callback for the cancellation token so that we can send a cancellation request to the workers.

```csharp
if (_cancelCapabilityEnabled)
{
context.CancellationToken.Register(() => SendInvocationCancel(invocationRequest.InvocationId));
}
```

`.Register` returns a disposable - should we be disposing it?

[CancellationTokenRegistration](https://learn.microsoft.com/en-us/dotnet/api/system.threading.cancellationtokenregistration?view=net-7.0)

- [ ] Investigate to see if we should be disposing the `CancellationTokenRegistration`
- [ ] If yes, implement changes to dispose the registration once we know the request in scope has been completed

Start in GrpcWorkerChannel.cs at the invocation request method and review the CancellationToken.Register call and its CancellationTokenRegistration documentation. Determine whether the registration remains in scope after the invocation request completes; if disposal is needed, implement it and verify the request lifecycle handles completion correctly.

Written by the indexing model from the issue text.