Aborting a sweep with a long running `DelayStimulus`

[Andrew Keller]

• Currently the sweep will kind of hang until the delay finishes, in a weird state where the status is Aborted but the job is still listed as the running job.
• Additionally, if the stimulus' t0 is set to -Inf then the job will be reported as Done with a progress that is less than 100%.
• Should we make an Aborting status in addition to Aborted?