worker: Possible infinite loop when JWT verification fails

If there's a problem in JWT verification, we think there's a case where the claim loop will continue to run infinitely even though the socket is disconnected. This sort of ends up with a zombie worker which will noiselessly fail to claim forever.

And that makes sense because the backoffloop will just trap an error and back off.

To reproduce:

• in the lightning mock, set the not before token on the JWT to sometime in the future
• This will trigger JWT validation to fail in the worker
• This will exit the claim channel but also continue to run the backoff loop without doing anything

Need to investigate this

Start by reproducing the failure in the lightning mock with the JWT not-before token set in the future. Trace the worker's claim channel and backoff loop to determine why failed verification continues after the socket disconnects; done means the worker stops instead of retrying forever.