FR: `ExecTracker` should be able to mock jet outputs, or at least "continue after abort"

[apoelstra]

For debugging/tracing it would be nice to be able to edit input/output data in the bit machine.

[apoelstra]

BlockstreamResearch/hal-simplicity#23

[apoelstra]

In general "continue after abort" is hard, but for the specific case of jet_verify it's easy.